* [[https://blogs.oracle.com/sql/improve-sql-query-performance-by-using-bind-variables|Improve SQL Query Performance by Using Bind Variables - All Things SQL]]
* [[https://dach.tdsynnex.com/blog/ch/wp-content/uploads/sites/4/2023/04/2022.11.15_OracleOnPowerTuningConsiderations_CPU_Memory_PSUG2022.pdf|Oracle Database on IBM Power with AIX Best Practices (Part 1: Memory and CPU)]]
* [[https://www.linkedin.com/pulse/19-great-things-you-can-do-vactivesessionhistory-part-merav-kedem|19 Great Things You Can Do With V$ACTIVE_SESSION_HISTORY (Part 1)]]
* [[https://blogs.oracle.com/connect/post/beginning-performance-tuning-trace-your-steps|How to trace SQL sessions to identify Oracle Database bottlenecks - Arup Nanda]]
* [[https://support.oracle.com/epmos/faces/DocumentDisplay?id=33089.1|TROUBLESHOOTING: Possible Causes of Poor SQL Performance (Doc ID 33089.1)]]
* [[https://docs.oracle.com/database/121/TGSQL/tgsql_histo.htm#TGSQL95033|Histograms - Database SQL Tuning Guide - oracle.com]]
* [[https://www.informit.com/articles/article.aspx?p=1400612&seqNum=5|Oracle Performance Tuning: A Methodical Approach - informit.com]]
* [[https://oracle-base.com/articles/12c/adaptive-plans-12cr1|Adaptive Plans in Oracle Database 12c - oracle-base.com]]
* [[https://asktom.oracle.com/pls/apex/f?p=100:11:0::::p11_question_id:9422487749968|Why full table scans are not always bad - asktom.com]]
* [[https://magnusjohanssontuning.wordpress.com/2017/10/09/high-buffer-gets-for-small-delete/|High buffer gets for small delete - Oracle Tuning by Magnus Johansson]]
* [[https://magnusjohanssontuning.wordpress.com|Oracle Tuning by Magnus Johansson]]
* [[https://www.dba-career.com/2017/07/awr-addr-and-ash-reports-quick.html|Difference between AWR, ADDM and ASH Reports in Oracle Performance Tuning]]
* [[http://www.petefinnigan.com/ramblings/how_to_set_trace.htm|How to set trace for others sessions, for your own session and at instance level]]
* [[https://support.oracle.com/epmos/faces/DocumentDisplay?id=199083.1|Master Note: SQL Query Performance Overview (Doc ID 199083.1)]]
* [[http://juliandyke.com/Presentations/Presentations.php|Advanced Oracle presentations - Julian Dyke]]
* [[https://support.oracle.com/epmos/faces/DocumentDisplay?id=443746.1|Metalink AMM Note 443746.1]]
* [[https://community.oracle.com/thread/858909|CBO not picking correct indexes or doing Full Scans]]
* [[https://docs.oracle.com/database/121/ADMIN/memory.htm#ADMIN00207|Oracle 12c documentation: Memory Management]]
* [[http://perfhints.blogspot.com/2009/02/oracle-11g-memory-management-made.html|Memory Management through the versions]]
* [[http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1137385000346840516|Automatic Memory Management discussion with Tom Kyte]]
* [[http://www.oracle-base.com/articles/11g/automatic-memory-management-11gr1.php| Automatic Memory Management from ORACLE_BASE]]
* [[https://books.google.be/books/about/Troubleshooting_Oracle_Performance.html?id=-cjAAwAAQBAJ&printsec=frontcover&source=kp_read_button&redir_esc=y#v=onepage&q&f=false|Troubleshooting Oracle Performance - A methodical approach]]
* [[https://www.oraclenext.com/2018/03/reading-and-understanding-awr-report.html|Reading and Understanding AWR Report for I/O or Disk latency]]
* [[http://logicalread.solarwinds.com/oracle-contention-for-shared-pool-and-library-cache-latches-mc01/#.Vj80XJRNS9j|How Parsing in Oracle Causes Contention for Shared Pool and Library Cache Latches]]
* [[https://www.dba-career.com/2017/07/awr-addr-and-ash-reports-quick.html|Difference between AWR, ADDM and ASH Reports in Oracle Performance Tuning]]
* [[http://www.petefinnigan.com/ramblings/how_to_set_trace.htm|How to set trace for others sessions, for your own session and at instance level]]
* [[https://support.oracle.com/epmos/faces/DocumentDisplay?id=199083.1|Master Note: SQL Query Performance Overview (Doc ID 199083.1)]]
* [[http://juliandyke.com/Presentations/Presentations.php|Advanced Oracle presentations - Julian Dyke]]
* [[https://support.oracle.com/epmos/faces/DocumentDisplay?id=443746.1|Metalink AMM Note 443746.1]]
* [[https://community.oracle.com/thread/858909|CBO not picking correct indexes or doing Full Scans]]
* [[https://docs.oracle.com/database/121/ADMIN/memory.htm#ADMIN00207|Oracle 12c documentation: Memory Management]]
* [[http://perfhints.blogspot.com/2009/02/oracle-11g-memory-management-made.html|Memory Management through the versions]]
* [[http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1137385000346840516|Automatic Memory Management discussion with Tom Kyte]]
* [[http://www.oracle-base.com/articles/11g/automatic-memory-management-11gr1.php| Automatic Memory Management from ORACLE_BASE]]
* [[https://books.google.be/books/about/Troubleshooting_Oracle_Performance.html?id=-cjAAwAAQBAJ&printsec=frontcover&source=kp_read_button&redir_esc=y#v=onepage&q&f=false|Troubleshooting Oracle Performance - A methodical approach]]
* [[https://www.oraclenext.com/2018/03/reading-and-understanding-awr-report.html|Reading and Understanding AWR Report for I/O or Disk latency]]
* [[http://logicalread.solarwinds.com/oracle-contention-for-shared-pool-and-library-cache-latches-mc01/#.Vj80XJRNS9j|How Parsing in Oracle Causes Contention for Shared Pool and Library Cache Latches]]
* [[Tuning]]
* [[http://juliandyke.com/Presentations/Presentations.php#AdvancedDiagnosticsRevisited|juliandyke.com - Advanced Diagnostics (including oradebug 10046 10053 etc...)]]
Scripts
* [[https://dbaclass.com/monitor-your-db/|Monitoring scripts from dbaclass.com]]
* [[https://github.com/freddenis/oracle-scripts|Collection of scripts by Fred Denis, the unknowndba.blogspot.com]]
* [[Snippets]]
* [[Handy Scripts]]
* [[Tuning]]
* [[http://juliandyke.com/Presentations/Presentations.php#AdvancedDiagnosticsRevisited|juliandyke.com - Advanced Diagnostics (including oradebug 10046 10053 etc...)]]
* [[https://www.informit.com/articles/article.aspx?p=1400612&seqNum=5|Oracle Performance Tuning: A Methodical Approach - Stage 3: Reducing Physical IO]]
* [[https://renenyffenegger.ch/notes/development/databases/Oracle/installed/packages/dbms/xplan/api/display/cursor/index|Gather plan stats in a hint and show with DBMS_XPLAN.DISPLAY_CURSOR]]
==== Why was my query fast yesterday and super slow today? ====
* [[https://mikesmithers.wordpress.com/2022/11/21/flipping-plans-retrieving-past-execution-plans-from-awr/|Execution plan has changed for a query. How to find the old and the new]]
Maybe the stats are stale, maybe something happened to global temporary tables, maybe something else happened but now the query that was super fast yesterday is now running like a pig. Could be that the execution plan has changed.
I'm not going to rehash all that was said by the AntiKyte so I'll just put the main points here in case his article is removed.
sho parameter awr
NAME TYPE VALUE
--------------------------- ------- -----
awr_pdb_autoflush_enabled boolean FALSE
awr_pdb_max_parallel_slaves integer 10
awr_snapshot_time_offset integer 0
Allow autoflush
alter system set awr_pdb_autoflush_enabled = true;
Adjust the snapshot interval
select * from cdb_hist_wr_control;
begin
dbms_workload_repository.modify_snapshot_settings(
interval => 10,
topnsql => 'MAXIMUM');
end;
/
Make a big table
create table chunky as select * from dba_objects;
begin
for i in 1..100 loop
insert into chunky
select * from dba_objects;
-- commit after each iteration as we're a bit tight
-- on resources
commit;
end loop;
end;
/
create index chunky_owner on chunky(owner);
exec dbms_stats.gather_table_stats(user, 'CHUNKY');
Start a new snapshot
exec dbms_workload_repository.create_snapshot;
Find the sql_id from the the v$sql table
select sql_id, sql_text
from v$sql
where sql_text like 'select%/*%slide 1%*/%'
and sql_text not like '%v$sql%'
/
Create another snapshot and ennsure a different plan is generated by hiding the index
exec dbms_workload_repository.create_snapshot;
alter index chunky_owner invisible;
Rerun the query. They should appear in different snapshots.
Check the awr history tables to see if we can see more than one plan
select
snap.snap_id,
snap.instance_number,
begin_interval_time,
sql_id,
plan_hash_value,
nvl(executions_delta,0) execs,
(elapsed_time_delta/decode(nvl(executions_delta,0),0,1,executions_delta))/1000000 avg_etime,
(buffer_gets_delta/decode(nvl(buffer_gets_delta,0),0,1,executions_delta)) avg_lio
from dba_hist_sqlstat stat, dba_hist_snapshot snap
where sql_id = '&sql_id.'
and snap.snap_id = stat.snap_id
and snap.instance_number = stat.instance_number
and executions_delta > 0
order by 3
/
List the plans
select *
from dba_hist_sql_plan
where sql_id = '&sql_id.'
/
or
select *
from table ( dbms_xplan.display_workload_repository ( sql_id => '&sql_id.'
, plan_hash_value => &plan_hash_id
)
);
==== Top Program-Module-Action ====
From [[https://www.linkedin.com/pulse/19-great-things-you-can-do-vactivesessionhistory-part-merav-kedem|19 Great Things You Can Do With V$ACTIVE_SESSION_HISTORY (Part 1)]]
set lines 200 pages 100
col program for a42
col module for a42
col action for a42
select program
, module
, action
, count(*) cnt
, 100*trunc(ratio_to_report(count(*)) over (),4) "%"
from v$active_session_history
where 1=1
and sample_time > sysdate-1/24
group by program
, module
, action
order by count(*) desc
fetch first 50 rows only
/
==== Top user activity ====
set lines 200 pages 100
col username for a20
select du.username
, count(*) cnt
, 100*trunc(ratio_to_report(count(*)) over (),4) "%"
from v$active_session_history vash
join dba_users du on vash.user_id = du.user_id
where 1=1
and vash.sample_time > sysdate-1/24
group by du.username
order by count(*) desc
fetch first 20 rows only
/
==== Top Events ====
set lines 200 pages 100
col wait_class for a20
select nvl(event,'CPU') event
, nvl(wait_class,'CPU') wait_class
, count(*) cnt
, 100*trunc(ratio_to_report(count(*)) over (),4) "%"
from v$active_session_history
where 1=1
and sample_time > sysdate-1/24
group by event
, wait_class
order by count(*) desc
fetch first 20 rows only
/
=== Top SQL ====
set lines 200 pages 100
col sql_opname for a20
select vash.sql_id
, vash.sql_opname
, count(*) cnt
, 100*trunc(ratio_to_report(count(*)) over (),4) "%"
, vs.sql_text
from v$active_session_history vash
left join v$sqlarea vs on vash.sql_id = vs.sql_id
where 1=1
and sample_time > sysdate-10/60/24
and vash.sql_id is not null
group by vash.sql_id
, vash.sql_opname
, vs.sql_text
order by count(*) desc
fetch first 20 rows only
/
==== Top accessed objects ====
set lines 200 pages 100
col owner for a32
col object_name for a32
select vash.current_obj# object_id
, do.owner
, do.object_name
, do.object_type
, count(*) cnt
, 100*trunc(ratio_to_report(count(*)) over (),4) "%"
from v$active_session_history vash
left join dba_objects do on vash.current_obj# = do.object_id
where sample_time > sysdate-1/24
and current_obj# > 0
group by vash.current_obj#
, do.owner
, do.object_name
, do.object_type
order by count(*) desc
fetch first 30 rows only
/
==== How much hard parsing ====
set lines 200 pages 100
col in_parse for a9
col in_hard_parse for a14
select in_parse
, in_hard_parse
, count(*) cnt
, 100*trunc(ratio_to_report(count(*)) over (),4) "%"
from v$active_session_history
where 1=1
and sample_time > sysdate-30/60/24
group by in_parse
, in_hard_parse
order by count(*) desc
/
==== Everything the database did in the past n minutes ====
select vash.sample_time
, vash.sql_id
, vash.top_level_sql_id
, nvl(vash.event,'CPU') event
, in_parse
, in_hard_parse
, vash.force_matching_signature
, t.exact_matching_signature
, t.sql_text
from v$active_session_history vash
left join v$sqlarea t on vash.sql_id=t.sql_id
where 1=1
and vash.top_level_sql_id is not null
--and vash.top_level_sql_id='c6xbvn0rt49n5' --in case you know the id
and sample_time > sysdate-(&minutes_back./60/24)
order by sample_time desc
/
==== Create a snapshot/dump of the current state of the database ====
Ref [[https://support.oracle.com/epmos/faces/DocumentDisplay?id=1594905.1|Note 1594905.1]]
* No connections posible to the database except for sysdba.
* Nothing suspicious in the alertlog.
* Filesystems not full.
Before restarting, create hang analysis and systemstate trace files with the current state so that Oracle Support can have a look and see what is wrong.
Use -prelim flag if connections using sysdba are not even possible
* Collect Hang Analysis 1
sqlplus [-prelim] / as sysdba
oradebug setmypid
oradebug unlimit
oradebug tracefile_name
oradebug hanganalyze 3
Wait 1 minute....
* Collect Hang Analysis 2
sqlplus / as sysdba
oradebug setmypid
oradebug unlimit
oradebug tracefile_name
oradebug hanganalyze 3
* Collect Systemstate dump
sqlplus / as sysdba
oradebug setmypid
oradebug unlimit
oradebug dump systemstate 258
or
oradebug dump systemstate 266
oradebug tracefile_name
* Generate and Check ADDM report, implement findings, re-test
SQL> @?/rdbms/admin/addmrpt.sql
==== Explain plan for a recently statement statement ====
This example is from [[https://renenyffenegger.ch/notes/development/databases/Oracle/installed/packages/dbms/xplan/api/display/cursor/index|René Nyffenegger]] showing how to do it with an SQL in the current session but it should work for any SQL.
In order to collect execution statistics for the SQL plan, the hint gather_plan_statistics is used
select
--+ gather_plan_statistics
-- find-this-statement-01
count(*) cnt
from
dba_objects a,
dba_objects b
where
a.created > b.created and
a.object_name > b.object_name
;
Find SQL_ID and child number of executed SQL statement
select
sql_id,
child_number,
sql_text
from
v$sql
where
sql_text like '%find-this-statement-01%' and
sql_text not like '%v$sql%';
With the sql_id and child number queried in the previous statement, we can now execute dbms_xplan.display_cursor
select
*
from
table(dbms_xplan.display_cursor(
sql_id => '1cb036z54s4hu',
cursor_child_no => 0,
format => 'ALLSTATS LAST'
));
The data that is formatted by dbms_xplan.display_cursor is found in v$sql_plan_statistics_all, v$sql, v$sql_plan and v$sql_shard.
==== Trace all SQL in the current session, sending output to a tracefile (.trc) ====
set lines 1000 pages 0
col stmt for a500
col sid new_value sid
col ser new_value ser
select sid sid
, serial# ser
from sys.v_$session
where sid in (select distinct sid from sys.v_$mystat)
/
begin
dbms_monitor.session_trace_enable (
session_id => &sid,
serial_num => &ser,
waits => true,
binds => true,
plan_stat => 'all_executions');
end;
/
select vr.value ||'/diag/rdbms/'||
-- sys_context('USERENV','DB_NAME') ||'/'||
-- sys_context('USERENV','INSTANCE_NAME') ||'/trace/'||
-- sys_context('USERENV','DB_NAME') ||'_ora_'||vp.spid||'.trc' tracefile_name
vd.db_unique_name ||'/'||
vi.instance_name ||'/trace/'||
vd.db_unique_name ||'_ora_'||vp.spid||'.trc' tracefile_name
from v$session vs
, v$parameter vr
, v$process vp
, v$database vd
, v$instance vi
where vr.name = 'diagnostic_dest'
and vs.sid = &sid
and vp.addr = vs.paddr
/
==== SQLTXPLAIN ====
SQLTXPLAIN (SQLT) Tool that helps to diagnose SQL statements performing poorly [[https://support.oracle.com/epmos/faces/DocumentDisplay?id=1614107.1|Note 1614107.1]]
==== Trace an SQL query ====
Useful additional information [[https://oracleyogi.wordpress.com/2015/12/26/10053-trace-demystified/|10053 trace demystified]]
alter session set tracefile_identifier='10053_&your_ref';
alter session set timed_statistics = true;
alter session set statistics_level=all;
alter session set max_dump_file_size = unlimited;
alter session set events '10053 trace name context forever, level 1';
explain plan for select count('x') from dba_segments;
alter session set events '10053 trace name context off';
alter session set tracefile_identifier='10046_&your_ref';
alter session set timed_statistics = true;
alter session set statistics_level=all;
alter session set max_dump_file_size = unlimited;
alter session set events '10046 trace name context forever,level 12';
rem execute the query for 30 minutes, then stop it
select count('x') from dba_segments;
select 'Verify Close' from dual;
alter session set events '10046 trace name context off';
exit;
Then find the trc files in the trace directory, probably in
ls -altr $ORACLE_BASE/diag/rdbms/${ORACLE_SID}/${ORACLE_SID}/trace/|egrep "(10046|10053)"
==== set event 10046 ====
alter system set events 'sql_trace [sql:&1] bind=&2, wait=&3'
/
With this event set every time this sqlid is executed it will be traced, Supply TRUE for binds and waits means they will be shown in the tracefiles as well. To disable the event, run
alter system set events 'sql_trace [sql:&1] off'
/
tkprof the tracefile
tkprof trace.trc /tmp/trace.trc.tkprof sys=y
sys=y means that it will include all sql executed, also what is called recursive sql. Recursive sql is sql executed on behalf of the executed sql.
==== How to Diagnose Slow TNS Listener / Connection Performance ====
Ref: [[https://orasg.wordpress.com/2015/10/31/how-to-diagnose-slow-tns-listener-connection-performance/|How to Diagnose Slow TNS Listener / Connection Performance - Hanh Nguyen]]
* [[Listener]]
==== Tracing the Cost Based Optimiser (CBO) ====
This is the Cost-based Optimizer trace. This trace really tells you ‘why did the CBO process this explain plan’…it goes into considerable detail on the hard parsing process
This is the syntax to start and stop this trace. The trace files are all created in the ‘BACKGROUND_DUMP_DEST’ location
alter session set events '10053 trace name context forever';
Run sql here
alter session set events '10053 trace name context off';
==== Get the total amount of memory currently in use by databases on the server ====
./all_db_do "select instance_name,round((select max(p.pga_max_mem)/1024/1024 mem_used from v\$process p)+(select sum(value)/1024/1024 from v\$sga)) total_mem_size_in_mb from v\$instance;"
==== Tanel Poder's session snapper ====
* [[http://tech.e2sn.com/oracle-scripts-and-tools/session-snapper|e2sn.com]]
==== More from Tanel Poder ====
* [[https://blog.tanelpoder.com/2008/08/07/the-simplest-query-for-checking-whats-happening-in-a-database/|The simplest query for checking what’s happening in a database]]
* [[https://github.com/tanelpoder/tpt-oracle/|Tanel Poder scripts on Github]]
==== Set trace in another session using DBMS_SYSTEM ====
First lets set trace in SCOTT's session using the DBMS_SYSTEM package. Before we do let's turn on timed statistics so that the trace files get timing info and also set the dump file size so that there is plenty of room for the trace being generated.
exec dbms_system.set_bool_param_in_session(10,20,'timed_statistics',true);
exec dbms_system.set_int_param_in_session(10,20,'max_dump_file_size',2147483647);
exec dbms_system.set_sql_trace_in_session(10,20,true);
exec dbms_system.set_sql_trace_in_session(10,20,false);
A second way to set trace in another session - This time setting trace level as well\\
Events and trace levels:
* Level 0 = No statistics generated
* Level 1 = standard trace output including parsing, executes and fetches plus more.
* Level 2 = Same as level 1.
* Level 4 = Same as level 1 but includes bind information
* Level 8 = Same as level 1 but includes wait's information
* Level 12 = Same as level 1 but includes binds and waits
Turn on tracing
exec dbms_system.set_ev(10,20,10046,8,'');
Turn off tracing
exec dbms_system.set_ev(10,20,10046,0,'');
Yet another way - with dbms_support package\\
If not installed, do so with @?rdbms\admin\dbmssupp.sql
exec dbms_support.start_trace_in_session(10,20,waits=>true,binds=>false);
exec dbms_support.stop_trace_in_session(10,20);
=== Shared pool loaded objects ====
set lines 1000 pages 100
col owner for a20
col name for a30
col type for a12
select owner
, name
, type
, round(sharable_mem/1024,2) size_kb
, loads
, kept
, executions
, locks
, pins
from v$db_object_cache
where type in ('PROCEDURE', 'PACKAGE BODY', 'PACKAGE', 'FUNCTION', 'TRIGGER', 'VIEW')
order by sharable_mem desc
/
==== See the state of the SGA (which components are shrinking and growing) ====
set lines 1000 pages 100
col component for a25
col oper_type for a15
col oper_mode for a15
col parameter for a25
col status for a10
col start_time for a18
col end_time for a18
select component
, oper_type
, oper_mode
, parameter
, initial_size/1024/1024 init_MB
, target_size/1024/1024 target_MB
, final_size/1024/1024 final_MB
, status
, start_time
, end_time
from v$sga_resize_ops
/
set lines 80
On a system in trouble, errors will be seen when trying to grow a component...
COMPONENT OPER_TYPE OPER_MODE PARAMETER INIT_MB TARGET_MB FINAL_MB STATUS START_TIME END_TIME
------------------------------ ------------- --------- -------------------- ---------- ---------- ---------- --------- ------------------ ------------------
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:44 01-MAY-19 05:56:44
DEFAULT buffer cache SHRINK IMMEDIATE db_cache_size 224 208 224 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
DEFAULT buffer cache SHRINK IMMEDIATE db_cache_size 224 208 224 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
DEFAULT buffer cache SHRINK IMMEDIATE db_cache_size 224 208 224 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
DEFAULT buffer cache SHRINK IMMEDIATE db_cache_size 224 208 224 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
DEFAULT buffer cache SHRINK IMMEDIATE db_cache_size 224 208 224 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
DEFAULT buffer cache SHRINK IMMEDIATE db_cache_size 224 208 224 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
shared pool GROW IMMEDIATE shared_pool_size 928 944 928 ERROR 01-MAY-19 05:56:45 01-MAY-19 05:56:45
On a freshly started system everything is good...
COMPONENT OPER_TYPE OPER_MODE PARAMETER INIT_MB TARGET_MB FINAL_MB STATUS START_TIME END_TIME
------------------------- ------------- --------- ------------------------- ---------- ---------- ---------- --------- ------------------ ------------------
shared pool STATIC shared_pool_size 0 1024 1024 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
In-Memory Area STATIC inmemory_size 0 0 0 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
large pool STATIC large_pool_size 0 1056 1056 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
RECYCLE buffer cache STATIC db_recycle_cache_size 0 0 0 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
KEEP buffer cache STATIC db_keep_cache_size 0 0 0 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
java pool STATIC java_pool_size 0 48 48 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
streams pool STATIC streams_pool_size 0 0 0 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
DEFAULT buffer cache STATIC db_cache_size 0 928 928 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
ASM Buffer Cache STATIC db_cache_size 0 0 0 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
DEFAULT buffer cache INITIALIZING db_cache_size 928 928 928 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
DEFAULT 2K buffer cache STATIC db_2k_cache_size 0 0 0 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
DEFAULT 4K buffer cache STATIC db_4k_cache_size 0 0 0 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
DEFAULT 8K buffer cache STATIC db_8k_cache_size 0 0 0 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
DEFAULT 16K buffer cache STATIC db_16k_cache_size 0 0 0 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
DEFAULT 32K buffer cache STATIC db_32k_cache_size 0 0 0 COMPLETE 01-MAY-19 12:04:40 01-MAY-19 12:04:40
DEFAULT buffer cache SHRINK IMMEDIATE db_cache_size 928 864 864 COMPLETE 01-MAY-19 12:04:52 01-MAY-19 12:04:52
DEFAULT buffer cache GROW DEFERRED db_cache_size 864 944 944 COMPLETE 01-MAY-19 12:05:24 01-MAY-19 12:05:24
large pool SHRINK DEFERRED large_pool_size 1056 976 976 COMPLETE 01-MAY-19 12:05:24 01-MAY-19 12:05:24
==== How to create an ADDM report quickly ====
From [[http://www.runningoracle.com/product_info.php?cPath=1_67|Running Oracle - AWR]]
set lines 1000 pages 100
select a.execution_end, b.type, b.impact, d.rank, d.type,
'Message : '||b.message MESSAGE,
'Command To correct: '||c.command COMMAND,
'Action Message : '||c.message ACTION_MESSAGE
From dba_advisor_tasks a, dba_advisor_findings b,
Dba_advisor_actions c, dba_advisor_recommendations d
Where a.owner=b.owner and a.task_id=b.task_id
And b.task_id=d.task_id and b.finding_id=d.finding_id
And a.task_id=c.task_id and d.rec_id=c.rec_Id
And a.task_name like 'ADDM%' and a.status='COMPLETED'
and a.execution_end > sysdate - 1
Order by a.execution_end desc, rank desc;
==== See how evenly the physical reads and writes are spread over the datafiles ====
From [[http://www.runningoracle.com/product_info.php?cPath=1_68&products_id=85|runningoracle.com - Datafiles Disk I/O]]
The Physical design of the database assures optimal performance for DISK I/O. Storing the datafiles in different filesystems (Disks) is a good technique to minimize disk contention for I/O
set lines 1000
col perc_writes for a12
col perc_reads for a12
col name for a55
select name
, phyrds physical_reads
, round((ratio_to_report(phyrds) over ())*100, 2)|| '%' perc_reads
, phywrts physical_writes
, round((ratio_to_report(phywrts) over ())*100, 2)|| '%' perc_writes
, phyrds + phywrts total
from v$datafile df
, v$filestat fs
where df.file# = fs.file#
order by phyrds desc
/
==== How I/O is spread per filesystem ====
select filesystem
, round((ratio_to_report(reads) over ())*100, 2) || '%' perc_reads
, round((ratio_to_report(writes) over ())*100, 2) || '%' perc_writes
, round((ratio_to_report(total) over ())*100, 2) || '%' perc_total
from (
select filesystem
, sum(physical_reads) reads
, sum(physical_writes) writes
, sum(total) total
from (
select substr(name, 0, 25) filesystem
, phyrds physical_reads
, round((ratio_to_report(phyrds) over ())*100, 2)|| '%' perc_reads
, phywrts physical_writes
, round((ratio_to_report(phywrts) over ())*100, 2)|| '%' perc_writes
, phyrds + phywrts total
from v$datafile df
, v$filestat fs
where df.file# = fs.file#
order by phyrds desc
) a
group by filesystem
) b
order by round((ratio_to_report(total) over ())*100, 2) desc;
==== How I/O is spread for the datafiles of a specific tablespace ====
select df.name
, phyrds physical_reads
, round((ratio_to_report(phyrds) over ())*100, 2)|| '%' perc_reads
, phywrts physical_writes
, round((ratio_to_report(phywrts) over ())*100, 2)|| '%' perc_writes
, phyrds + phywrts total
from v$datafile df
, v$filestat fs
, ts$ t
where df.file# = fs.file#
and df.ts# = t.ts#
and t.name = 'tablespace_name'
order by phyrds desc;
==== Spotting I/O intensive SQL statements ====
From [[https://blog.rackspace.com/tuning-oracles-buffer-cache|rackspace.com - tuning oracles buffer cache
select *
from (
select executions
, buffer_gets
, disk_reads
, first_load_time
, sql_text
from v$sqlarea
order by disk_reads desc
)
where rownum < 11
/
==== Enable and disable session tracing using PL/SQL package ====
See also trace of a particular session_id in [[Datapump]] section.
exec dbms_monitor.session_trace_enable;
exec dbms_monitor.session_trace_disable;
exec dbms_monitor.database_trace_enable;
exec dbms_monitor.database_trace_disable;
exec dbms_monitor.client_id_trace_enable;
exec dbms_monitor.client_id_trace_disable;
exec dbms_monitor.serv_mod_act_trace_enable;
exec dbms_monitor.serv_mod_act_trace_disable;
==== Show database resource limits and current usage ====
set lines 1000 pages 100
select resource_name
, current_utilization
, max_utilization
, limit_value
from v$resource_limit
/
==== Show long-running SQL queries / statements ====
Long running means more than 10 minutes if last_call_et > 600 (adjust as necessary!)
set pages 1000 headi on underline off lines 1000
col username for a15
col program for a20
col osuser for a15
select distinct machine
, nvl(s.osuser,'no user') osuser
, s.username username
, s.sid sid
, s.serial# serial#
, (s.last_call_et/60) mins
, s.last_call_et secs
, s.program program
, s.sql_id sql_id
, q.sql_text sql_text
from v$session s
, v$sql q
where s.sql_id = q.sql_id
and status = 'ACTIVE'
and type != 'BACKGROUND'
and last_call_et > 600
order by sid
, serial#
/
==== Enable block change tracking (BCT) ====
alter database enable block change tracking;
==== Disable block change tracking (BCT) ====
alter database disable block change tracking;
==== Where is the block change tracking file? ====
select filename from v$block_change_tracking
/
==== Check if block change tracking (BCT) is enabled ====
select status from v$block_change_tracking
/
or
ps -ef | grep [c]twr
==== Show CPU Usage for Active Sessions ====
SET PAGESIZE 60
SET LINESIZE 300
COLUMN username FORMAT A30
COLUMN sid FORMAT 999,999,999
COLUMN serial# FORMAT 999,999,999
COLUMN "cpu usage (seconds)" FORMAT 999,999,999.0000
SELECT
s.username,
t.sid,
s.serial#,
SUM(VALUE/100) as "cpu usage (seconds)"
FROM
v$session s,
v$sesstat t,
v$statname n
WHERE
t.STATISTIC# = n.STATISTIC#
AND
NAME like '%CPU used by this session%'
AND
t.SID = s.SID
AND
s.status='ACTIVE'
AND
s.username is not null
GROUP BY username,t.sid,s.serial#
/
==== Show the Bind Variables for a Given sqlid ====
SET PAGESIZE 60
SET LINESIZE 300
COLUMN sql_text FORMAT A120
COLUMN sql_id FORMAT A13
COLUMN bind_name FORMAT A10
COLUMN bind_value FORMAT A26
SELECT
sql_id,
t.sql_text sql_text,
b.name bind_name,
b.value_string bind_value
FROM
v$sql t
JOIN
v$sql_bind_capture b using (sql_id)
WHERE
b.value_string is not null
AND
sql_id='&sqlid'
/
==== List the Most Resource Hungry SQL Statements ====
SET PAGESIZE 60
SET LINESIZE 300
COLUMN sql_text FORMAT A50
COLUMN reads_per_execution FORMAT 999,999,999
COLUMN buffer_gets FORMAT 999,999,999
COLUMN disk_reads FORMAT 999,999,999
COLUMN executions FORMAT 999,999,999
COLUMN sorts FORMAT 999,999,999
SELECT *
FROM (SELECT Substr(a.sql_text,1,50) sql_text,
Trunc(a.disk_reads/Decode(a.executions,0,1,a.executions)) reads_per_execution,
a.buffer_gets,
a.disk_reads,
a.executions,
a.sorts,
a.address,
a.sql_id
FROM v$sqlarea a
ORDER BY 2 DESC)
WHERE rownum <= &rows_to_by_displayed
/
==== Is stats gathering enabled? ====
column client_name format A55
SELECT client_name, status from dba_autotask_operation;
==== Check when the statistics advisor tasks ran ====
This shows the details of various advisor jobs
col name for a50
col owner_name for a10
col name for a40
select name
, ctime
, how_created
, owner_name
, name
from sys.wri$_adv_tasks
where 1=1
--and owner_name = 'SYS'
--and name in ('AUTO_STATS_ADVISOR_TASK','INDIVIDUAL_STATS_ADVISOR_TASK')
order by 2
gives something like...
NAME CTIME HOW_CREATED OWNER_NAME NAME
----------------------------------- --------------------------- ------------------------------ ---------- -----------------------------------
SYS_AUTO_SPCADV339041814082021 14-AUG-21 18:04:39 CMD SYS SYS_AUTO_SPCADV339041814082021
SYS_AUTO_SPCADV216002216082021 16-AUG-21 22:00:16 CMD SYS SYS_AUTO_SPCADV216002216082021
ADDM:141033772_1_15823 21-AUG-21 00:00:23 AUTO SYS ADDM:141033772_1_15823
SYS_AUTO_SPCADV522010021082021 21-AUG-21 00:01:23 CMD SYS SYS_AUTO_SPCADV522010021082021
ADDM:141033772_1_15831 21-AUG-21 08:00:41 AUTO SYS ADDM:141033772_1_15831
ADDM:141033772_1_15874 23-AUG-21 03:00:43 AUTO SYS ADDM:141033772_1_15874
ADDM:141033772_1_15880 23-AUG-21 09:01:01 AUTO SYS ADDM:141033772_1_15880
ADDM:141033772_1_15884 23-AUG-21 13:00:09 AUTO SYS ADDM:141033772_1_15884
ADDM:141033772_1_15906 24-AUG-21 11:00:09 AUTO SYS ADDM:141033772_1_15906
ADDM:141033772_1_15922 25-AUG-21 03:00:56 AUTO SYS ADDM:141033772_1_15922
ADDM:141033772_1_15932 25-AUG-21 13:00:20 AUTO SYS ADDM:141033772_1_15932
ADDM:141033772_1_15939 25-AUG-21 20:00:36 AUTO SYS ADDM:141033772_1_15939
SYS_AUTO_SPCADV151060126082021 26-AUG-21 01:06:52 CMD SYS SYS_AUTO_SPCADV151060126082021
ADDM:141033772_1_15946 26-AUG-21 03:00:56 AUTO SYS ADDM:141033772_1_15946
ADDM:141033772_1_15957 26-AUG-21 14:00:22 AUTO SYS ADDM:141033772_1_15957
...
ADDM:141033772_1_16360 12-SEP-21 09:00:53 AUTO SYS ADDM:141033772_1_16360
SYS_AUTO_SPCADV951040912092021 12-SEP-21 09:04:51 CMD SYS SYS_AUTO_SPCADV951040912092021
ADDM:141033772_1_16361 12-SEP-21 10:00:57 AUTO SYS ADDM:141033772_1_16361
SYS_AUTO_SPCADV557041012092021 12-SEP-21 10:04:57 CMD SYS SYS_AUTO_SPCADV557041012092021
ADDM:141033772_1_16362 12-SEP-21 11:00:59 AUTO SYS ADDM:141033772_1_16362
SYS_AUTO_SPCADV155041112092021 12-SEP-21 11:04:55 CMD SYS SYS_AUTO_SPCADV155041112092021
ADDM:141033772_1_16363 12-SEP-21 12:01:01 AUTO SYS ADDM:141033772_1_16363
SYS_AUTO_SPCADV759041212092021 12-SEP-21 12:04:59 CMD SYS SYS_AUTO_SPCADV759041212092021
ADDM:141033772_1_16364 12-SEP-21 13:00:04 AUTO SYS ADDM:141033772_1_16364
SYS_AUTO_SPCADV302051312092021 12-SEP-21 13:05:02 CMD SYS SYS_AUTO_SPCADV302051312092021
958 rows selected.
==== Check when statistics were last gathered ====
select owner,table_name,tablespace_name,to_char(LAST_ANALYZED,'DD-MON-YY HH24:MI:SS') LAST_ANALYZED from dba_tables where owner not in ('SYS','SYSTEM') order by LAST_ANALYZED
==== Gather more accurate statistics ====
default is 2
alter system set optimizer_dynamic_sampling = 4;
==== Check for stale statistics ====
set lines 200 pages 100
col table_owner for a15
col table_name for a40
select m.table_owner
, m.table_name
, m.timestamp
, sum(m.inserts)
, sum(m.updates)
, sum(m.deletes)
, t.num_rows
, t.last_analyzed
from sys.dba_tab_modifications m
, dba_tables t
where m.table_owner = t.owner
and m.table_name = t.table_name
group by m.table_owner
, m.table_name
, m.timestamp
, t.num_rows
, t.last_analyzed
order by 1,2,3
/
set lines 80
or
set lines 200 pages 200
col owner_table for a30
col partition_name for a20
select dt.owner||'.'||dt.table_name owner_table
, dtm.partition_name
, inserts+updates+deletes modified_rows, num_rows, last_analyzed
, case when num_rows = 0 then null
else (inserts+updates+deletes) / num_rows * 100
end percent_modified
from dba_tab_modifications dtm
join dba_tables dt
on dtm.table_name = dt.table_name
order by 6 desc
/
==== Export dictionary and fixed statistics ====
begin
dbms_stats.create_stat_table ( stattab => 'dic_stats'
, ownname => 'system'
);
dbms_stats.export_dictionary_stats ( stattab => 'dic_stats'
, statown => 'system'
);
dbms_stats.create_stat_table ( stattab => 'fix_stats'
, ownname => 'system'
);
dbms_stats.export_fixed_objects_stats ( stattab => 'fix_stats'
, statown => 'system'
);
end;
/
expdp userid='system/' dumpfile=rpainse_dic_stats.dmp reuse_dumpfiles=true logfile=rpainse_dic_stats.log tables='DIC_STATS' directory=data_pump_dir
expdp userid='system/' dumpfile=rpainse_fix_stats.dmp reuse_dumpfiles=true logfile=rpainse_fix_stats.log tables='FIX_STATS' directory=data_pump_dir
==== Delete existing fixed and dictionary stats and import new ones ====
This can be done before importing stats from another database. Maybe queries work faster on prod and the stats need copying over to dev or acc.
begin
dbms_stats.delete_dictionary_stats;
dbms_stats.delete_fixed_objects_stats;
end;
/
impdp userid='system/' dumpfile=rpainse_dic_stats.dmp logfile=impdp_rpainse_dic_stats.log directory=data_pump_dir
impdp userid='system/' dumpfile=rpainse_fix_stats.dmp logfile=impdp_rpainse_fix_stats.log directory=data_pump_dir
==== Copy the statistics from a single query from one database to another ====
* [[https://martincarstenbach.wordpress.com/2020/06/09/copying-a-sql-plan-baseline-from-one-database-to-another/|Copying a SQL Plan Baseline from one database to another - martincarstenbach.wordpress.com]]
=== Pack up the baseline ===
set serveroutput on
prompt prepare a SQL Plan Baseline for transport
prompt
accept v_table_name prompt 'enter the name of the staging table to be created: '
accept v_table_owner prompt 'enter the schema name where the staging table is to be created: '
accept v_sql_handle prompt 'which SQL handle should be exported? '
accept v_plan_name prompt 'enter the corresponding plan name: '
declare
v_packed_baselines number;
begin
dbms_spm.create_stgtab_baseline(
table_name => '&v_table_name',
table_owner => '&v_table_owner');
v_packed_baselines := dbms_spm.pack_stgtab_baseline(
table_name => '&v_table_name',
table_owner => '&v_table_owner',
sql_handle => '&v_sql_handle',
plan_name => '&v_plan_name');
dbms_output.put_line(v_packed_baselines || ' baselines have been staged in &v_table_owner..&v_table_name');
end;
/
* Export the table, copy it over and import it into the destination database.
=== Unpack the baseline ===
var num_unpacked number
begin
:num_unpacked := dbms_spm.unpack_stgtab_baseline(
table_name => '&table_name',
table_owner => '&table_owner');
end;
/
print :num_unpacked
* Check it is there
select sql_handle, plan_name, origin, enabled, accepted, fixed from dba_sql_plan_baselines;
==== Gather database stats ====
Some helpful stuff on statistics gathering [[http://dba-tips.blogspot.co.uk/2012/11/all-about-statistics-in-oracle.html|here]]
- !/usr/bin/ksh
sqlplus / as sysdba << EOSQL
exec dbms_stats.gather_database_stats( estimate_percent=>dbms_stats.auto_sample_size, degree => 8 );
EOSQL
==== Setup a job to run gather statistics as a one-off job ====
begin
dbms_scheduler.create_job ( job_name => '"sys"."gather_fixed_object_stats_one_time"'
, job_type => 'PLSQL_BLOCK'
, job_action => 'begin dbms_stats.gather_fixed_object_stats; end;'
, start_date => sysdate+7
, auto_drop => true
, comments => 'gather fixed object stats one time'
);
dbms_scheduler.enable ( name => '"sys"."gather_fixed_object_stats_one_time"' );
end;
/
==== Gather dictionary and fixed objects statistics ====
A common problem when certain queries take a long time - a particular culprit is dba_free_space.\\
In this case also check the dba_recyclebin and purge it or disable it (at least on production) if not required.\\
The problem stems from queries doing a full table scan on x$ktfbue (and executing gather_fixed_object_stats didn't help as this table is specifically excluded from the gather!). The full story can be read [[https://jonathanlewis.wordpress.com/2019/08/08/free-space-3/|here by Jonathon Lewis]]
A rejigged query (using hints) was used in the past to speed up dba_free_space. This was provided by Oracle for 12.1.0.2
create or replace view DBA_FREE_SPACE
(TABLESPACE_NAME, FILE_ID, BLOCK_ID,
BYTES, BLOCKS, RELATIVE_FNO)
as
select ts.name, fi.file#, f.block#,
f.length * ts.blocksize, f.length, f.file#
from sys.ts$ ts, sys.fet$ f, sys.file$ fi
where ts.ts# = f.ts#
and f.ts# = fi.ts#
and f.file# = fi.relfile#
and ts.bitmapped = 0
union all
select /*+ ordered use_nl(f) use_nl(fi) */
ts.name, fi.file#, f.ktfbfebno,
f.ktfbfeblks * ts.blocksize, f.ktfbfeblks, f.ktfbfefno
from sys.ts$ ts, sys.x$ktfbfe f, sys.file$ fi
where ts.ts# = f.ktfbfetsn
and f.ktfbfetsn = fi.ts#
and f.ktfbfefno = fi.relfile#
and ts.bitmapped <> 0 and ts.online$ in (1,4) and ts.contents$ = 0
union all
select /*+ ordered use_nl(u) use_nl(fi) */
ts.name, fi.file#, u.ktfbuebno,
u.ktfbueblks * ts.blocksize, u.ktfbueblks, u.ktfbuefno
from sys.recyclebin$ rb, sys.ts$ ts, sys.x$ktfbue u, sys.file$ fi
where ts.ts# = rb.ts#
and rb.ts# = fi.ts#
and u.ktfbuefno = fi.relfile#
and u.ktfbuesegtsn = rb.ts#
and u.ktfbuesegfno = rb.file#
and u.ktfbuesegbno = rb.block#
and ts.bitmapped <> 0 and ts.online$ in (1,4) and ts.contents$ = 0
union all
select ts.name, fi.file#, u.block#,
u.length * ts.blocksize, u.length, u.file#
from sys.ts$ ts, sys.uet$ u, sys.file$ fi, sys.recyclebin$ rb
where ts.ts# = u.ts#
and u.ts# = fi.ts#
and u.segfile# = fi.relfile#
and u.ts# = rb.ts#
and u.segfile# = rb.file#
and u.segblock# = rb.block#
and ts.bitmapped = 0
/
Another table that struggles can be rman_backup_job_details.
Stats on the sys X$ tables under the V$ views are not automatically gathered. Furthermore, once gatherd, they persist across instance restarts. Having no stats (uses defaults) is better than having bad stats. Fixed object stats should be gathered when the database is under load so that the optimiser chooses plans based on a representative load.\\
Noticable performance issues on DBA_FREE_SPACE, V$RMAN_STATUS, V$RMAN_BACKUP_JOB_DETAILS can be fixed by gathering these stats.\\
How to Gather Statistics on Objects Owned by the ‘SYS’ User and ‘Fixed’ Objects ([[https://support.oracle.com/epmos/faces/DocumentDisplay?id=457926.1|Doc ID 457926.1]])\\
Fixed Objects Statistics (GATHER_FIXED_OBJECTS_STATS) Considerations ([[https://support.oracle.com/epmos/faces/DocumentDisplay?id=798257.1|Doc ID 798257.1]])\\
Other relevant MOS notes relating to gathering fixed objest stats include:
NOTE:375386.1 - Rman Backup is Very Slow selecting from V$RMAN_STATUS\\
NOTE:748251.1 - EM Agent DBSNMP Using Up Excessive Temp Space In Database\\
BUG:7430745 - ORA-1422 DBMS_STATS.GATHER_TABLE_STATS ON X$KTFBUE ON 10.2.0.4\\
NOTE:1392603.1 - AWR or STATSPACK Snapshot collection extremely slow in 11gR2\\
BUG:5259025 - THE FIXED TABLE X$KTFBUE HAS NO STATISTICS\\
BUG:5880432 - QUERYING V$ACCESS CONTENTS ON LATCH: LIBRARY CACHE DRAWBACKS PERFORMANCE\\
NOTE:247611.1 - Known RMAN Performance Problems\\
NOTE:373152.1 - Rman Slow Performance on Exit\\
BUG:5247609 - RMAN SLOW PERFORMANCE DURING REGISTER DATABASE/OPEN RESETLOGS\\
NOTE:465787.1 - How to: Manage CBO Statistics During an Upgrade from 10g or 9i into 11g/12c\\
NOTE:743507.1 - How to Benefit from Automatic Maintenance Tasks Following the Removal of the GATHER_STATS_JOB in 11g and Onward?\\
NOTE:357765.1 - Rman uses a lot Of Temporary Segments ORA-1652: Unable To Extend Temp Segment\\
NOTE:1637294.1 - Some Fixed Tables(X$) are Missing CBO Statistics\\
NOTE:1355608.1 - Why Do Some Fixed Tables Not Have Optimizer Statistics?\\
NOTE:294346.1 - Running GATHER_FIXED_OBJECTS_STATS is very slow\\
The current stats can be exported first in case the results of gathering are worse!
exec dbms_stats.drop_stat_table('system','fixed_stats_table');
exec dbms_stats.create_stat_table('system','fixed_stats_table');
exec dbms_stats.export_fixed_objects_stats ( statown => 'system', stattab => 'fixed_stats_table' );
expdp userid=system/****** tables=system.fixed_stats_table dumpfile=20200120_EBST_fixed_stats_table.dmp logfile=expdp_20200120_EBST_fixed_stats_table.log
exec dbms_stats.gather_dictionary_stats;
exec dbms_stats.gather_fixed_objects_stats;
==== Stats are not gathered on fixed table X$KTFBUE ====
From a study by Jonathon Lewis... [[https://jonathanlewis.wordpress.com/2019/08/08/free-space-3/]]
...
Part of the problem, of course, is that x$ktfbue is one of the objects that Oracle skips when you gather “fixed object” stats – it can be a bit expensive for exactly the reason that querying it can be expensive, all those single block segment header reads.
...
select table_name, num_rows, avg_row_len, sample_size, last_analyzed
from dba_tab_statistics
where owner = 'SYS'
and table_name = 'X$KTFBUE'
/
begin
dbms_stats.gather_table_stats('SYS','X$KTFBUE');
end;
/
==== Compress indexes to take up less space in the buffer cache ====
select blocks from dba_segments where segment_name = '&INDEX_NAME';
select index_name, compression from dba_indexes where index_name = '&INDEX_NAME';
alter index &INDEX_NAME rebuild compress advanced high;
==== Gather schema statistics ====
begin
dbms_stats.gather_schema_stats ( ownname => 'FEUK_SCR'
, options => 'gather auto'
, estimate_percent => 100
, degree => 6
, method_opt => 'for all indexed columns'
, cascade => true
);
end;
/
==== Gather table statistics ====
BEGIN dbms_stats.gather_table_stats(ownname =>'FEUK_PRF',tabname=>'TD_NOTE',estimate_percent=>20,cascade=>true,degree=>6,METHOD_OPT=>'FOR ALL COLUMNS SIZE 100' ); END;
==== Show any events set in database ====
set serveroutput on
declare
event_level number;
begin
dbms_output.enable(null);
dbms_output.put_line ('Event list');
dbms_output.put_line ('----------');
for i in 10000..10999 loop
sys.dbms_system.read_ev(i,event_level);
if (event_level > 0) then
dbms_output.put_line('Event '||to_char(i)||' set at level '|| to_char(event_level));
end if;
end loop;
end;
/
==== Show all Oracle hidden parameters ====
set pages 100 lines 300
col ksppinm for a50
col ksppstvl for a50
select ksppinm
, ksppstvl
from x$ksppi a
, x$ksppsv b
where 1=1
and a.indx=b.indx
and substr(ksppinm,1,1) = '_'
order by ksppinm
/
==== How Can we Run SQL Tuning Advisor For A SQL ID In Oracle Database? ====
* [[https://www.funoracleapps.com/2022/01/how-can-we-run-sql-tuning-advisor-for.html|How Can we Run SQL Tuning Advisor For A SQL ID In Oracle Database? - funoracleapps.com]]
Catch it while the statement is running...\\
1. Create Tuning Task
DECLARE
l_sql_tune_task_id VARCHAR2(100);
BEGIN
l_sql_tune_task_id := DBMS_SQLTUNE.create_tuning_task (
sql_id => '4g5ah8zr6thnb',
scope => DBMS_SQLTUNE.scope_comprehensive,
time_limit => 500,
task_name => '4g5ah8zr6thnb_tuning_task_cur',
description => 'Tuning task_cur for statement 4g5ah8zr6thnb');
DBMS_OUTPUT.put_line('l_sql_tune_task_id: ' || l_sql_tune_task_id);
END;
/
2. Execute Tuning task:
EXEC DBMS_SQLTUNE.execute_tuning_task(task_name => '4g5ah8zr6thnb_tuning_task_cur');
3. Get the Tuning advisor report.
set long 65536
set longchunksize 65536
set linesize 100
select dbms_sqltune.report_tuning_task('4g5ah8zr6thnb_tuning_task_cur') from dual;
4. Get list of tuning task present in database:\\
We can get the list of tuning tasks present in database from DBA_ADVISOR_LOG
SELECT TASK_NAME, STATUS FROM DBA_ADVISOR_LOG WHERE TASK_NAME='4g5ah8zr6thnb_tuning_task_cur' ;
5. Drop a tuning task:
execute dbms_sqltune.drop_tuning_task('4g5ah8zr6thnb_tuning_task_cur');
Method when the sql is not running. We can get the information from the AWR snaps when the query was ran.
SQL_ID =4g5ah8zr6thnb
Find the begin snap and end snap of the sql_id.
select a.instance_number inst_id, a.snap_id,a.plan_hash_value, to_char(begin_interval_time,'dd-mon-yy hh24:mi') btime, abs(extract(minute from (end_interval_time-begin_interval_time)) + extract(hour from (end_interval_time-begin_interval_time))*60 + extract(day from (end_interval_time-begin_interval_time))*24*60) minutes,
executions_delta executions, round(ELAPSED_TIME_delta/1000000/greatest(executions_delta,1),4) "avg duration (sec)" from dba_hist_SQLSTAT a, dba_hist_snapshot b
where sql_id='&sql_id' and a.snap_id=b.snap_id
and a.instance_number=b.instance_number
order by snap_id desc, a.instance_number;
From here we can get the begin snap and end snap of the sql_id.
begin_snap -> 6377
end_snap -> 6380
1. Create the tuning task:
DECLARE
l_sql_tune_task_id VARCHAR2(100);
BEGIN
l_sql_tune_task_id := DBMS_SQLTUNE.create_tuning_task (
begin_snap => 6377,
end_snap => 6380,
sql_id => '4g5ah8zr6thnb',
scope => DBMS_SQLTUNE.scope_comprehensive,
time_limit => 600,
task_name => '4g5ah8zr6thnb_AWR_tuning_task',
description => 'Tuning task for statement 4g5ah8zr6thnb in AWR');
DBMS_OUTPUT.put_line('l_sql_tune_task_id: ' || l_sql_tune_task_id);
END;
/
2. Execute the tuning task:
EXEC DBMS_SQLTUNE.execute_tuning_task(task_name => '4g5ah8zr6thnb_AWR_tuning_task');
3. Get the tuning task recommendation report
SET LONG 10000000;
SET PAGESIZE 100000000
SET PAGESIZE 24
SET LINESIZE 200
SELECT DBMS_SQLTUNE.report_tuning_task('4g5ah8zr6thnb_AWR_tuning_task') AS recommendations FROM dual;
==== Find the sessions consuming a high amount Temporary space ====
* [[https://www.funoracleapps.com/2021/06/query-to-find-session-consuming-high.html|Query to find the session consuming high Temp TableSpace - funoracleapps.com]]
Check the current status of the temporary tablespaces
select tablespace_name
, tablespace_size/1024/1024 "Total Space MB"
, allocated_space/1024/1024 "Alloc Space MB"
, free_space/1024/1024 "Free Space MB"
from dba_temp_free_space
/
select s.sid
, s.username
, u.tablespace
, s.sql_hash_value||' or '||u.sqlhash hash_value
, u.segtype
, u.contents
, u.blocks
from v$session s
, v$tempseg_usage u
where s.saddr=u.session_addr
and u.tablespace=upper('&tablespace_name')
order by u.blocks desc
/
Then for the sid and schema, run this. I wish I knew what it did!
select hash_value
, sorts
, rows_processed/executions
from v$sql
where hash_value in (select hash_value from v$open_cursor where sid=&sid)
and sorts > 0
and parsing_schema_name=upper('&schema_name')
order by rows_processed/executions
/
==== How much memory is being used by processes (PGA memory)? ====
* [[https://www.spotonoracle.com/?p=267|Tracking down PGA memory leak – a walkthrough - www.spotonoracle.com]]
* [[https://tanelpoder.com/2014/03/26/oracle-memory-troubleshooting-part-4-drilling-down-into-pga-memory-usage-with-vprocess_memory_detail/|Oracle Memory Troubleshooting, Part 4: Drilling down into PGA memory usage with V$PROCESS_MEMORY_DETAIL - Tanel Poder]]
* [[https://github.com/tanelpoder/tpt-oracle/blob/master/pmem.sql|Show process memory usage breakdown - lookup by process SPID]]
* [[https://support.oracle.com/epmos/faces/DocumentDisplay?id=822527.1|How To Find Where The Memory Is Growing For A Process (Doc ID 822527.1)]]
* [[https://dioncho.wordpress.com/2009/06/09/707/#comments|Troubleshooting PGA leak with PGA heap dump - Dion Cho – Oracle Performance Storyteller]]
set lines 1000 pages 100
col PGA_USED_MEGS for 999,999,990
col PGA_ALLOC_MEGS for 999,999,990
col PGA_FREEABLE_MEGS for 999,999,990
col PGA_MAX_MEGS for 999,999,990
compute sum of PGA_USED_MEGS on report
compute sum of PGA_ALLOC_MEGS on report
compute sum of PGA_MAX_MEGS on report
break on report
SELECT PROGRAM, (PGA_USED_MEM/1024/1024) PGA_USED_MEGS, (PGA_ALLOC_MEM/1024/1024) PGA_ALLOC_MEGS, (PGA_FREEABLE_MEM/1024/1024) PGA_FREEABLE_MEGS, (PGA_MAX_MEM/1024/1024) PGA_MAX_MEGS
FROM V$PROCESS
order by 2
/
==== or PGA memory with a bit more surrounding info ...temporary tablespace usage also ====
set lines 1000 pages 2000 trims on feed on newpa none
col username head "Username" for a18
col osuser head "O/S User" for a12
col sid_ser head "sid_ser" for a12
col ospid head "O/S pid" for a8
col logontime head "Logged on" for a15
col timenow head "Time now" for a15
col program head "Program" for a30 trunc
col machine head "Machine" for a18 trunc
col port head "Port" for 999999
col status head "Status" for a10
col cpu_secs head "CPU (s)" for 99990D9
col max_megs head "Max MB" for 99990D9
col alloc_megs head "Alloc MB" for 99990D9
col used_megs head "Used MB" for 99990D9
col freeable_megs head "Freeable" for 99990D9
col temp_used head "Temp MB" for 99990D9
col timenow nopri
compute sum of alloc_megs on report
compute sum of used_megs on report
compute sum of freeable_megs on report
break on report
with temp_usage as (
select su.session_addr session_addr
, s.sid||'_'||s.serial# sid_ser
, sum(su.blocks)*tbs.block_size/1024/1024 mb_used
, su.tablespace tablespace
from v$session s
, v$sort_usage su
, dba_tablespaces tbs
where 1=1
and s.saddr = su.session_addr
and su.tablespace = tbs.tablespace_name
group by su.session_addr
, s.sid
, s.serial#
, tbs.block_size
, su.tablespace
)
SELECT nvl(s.username,'BACKGROUND') username
, s.osuser osuser
, s.sid||','||s.serial# sid_ser
, p.spid ospid
, to_char(logon_time,'YYYYMMDDHH24MISS') logontime
, to_char(sysdate,'YYYYMMDDHH24MISS') timenow
, s.program program
, s.machine machine
, s.port port
, s.status status
, round((ss.value/1000),2) cpu_secs
, round(pga_max_mem/1024/1024) max_megs
, round(pga_alloc_mem/1024/1024) alloc_megs
, round(pga_used_mem/1024/1024) used_megs
, round(pga_freeable_mem/1024/1024) freeable_megs
, tu.mb_used temp_used
from v$process p
, v$session s
, v$sesstat ss
, v$statname sn
, temp_usage tu
where p.addr = s.paddr
and s.sid = ss.sid
and ss.statistic# = sn.statistic#
and sn.name = 'CPU used by this session'
and s.saddr = tu.session_addr(+)
order by pga_used_mem desc
/
set lines 80
==== SGA and PGA historic usage per hour (or snapshot interval) ====
set lines 1000 pages 5000 trims on
col instance_name head "Instance" for a9
col sga head "SGA(Mb)" for 9,990.9
col pga head "PGA(Mb)" for 9,990.9
col tot head "Total" for 99,990.9
col datetime head "Date" for a21
select i.instance_name instance_name
, sga.allocated sga
, pga.allocated pga
, (sga.allocated+pga.allocated) tot
, ' '||to_char(trunc(sn.end_interval_time,'mi'),'DD-MON-YY HH24:MI:SS') datetime
from (
select snap_id
, instance_number
, round(sum(bytes)/1024/1024/1024,3) allocated
from dba_hist_sgastat
group by snap_id
, instance_number
) sga
, (
select snap_id
, instance_number
, round(sum(value)/1024/1024/1024,3) allocated
from dba_hist_pgastat where name = 'total PGA allocated'
group by snap_id
, instance_number
) pga
, dba_hist_snapshot sn
, v$instance i
where sn.snap_id = sga.snap_id
and sn.instance_number = sga.instance_number
and sn.snap_id = pga.snap_id
and sn.instance_number = pga.instance_number
and sn.instance_number = i.instance_number
order by sn.end_interval_time desc
, sn.instance_number
/
set lines 80
==== Tuning PGA_AGGREGATE_TARGET ====
* [[https://docs.oracle.com/database/121/TGDBA/tune_pga.htm#GUID-C8C6D009-CF38-4996-AD0E-D97CE0CECE3D]]
SELECT ROUND(pga_target_for_estimate/1024/1024) target_mb,
estd_pga_cache_hit_percentage cache_hit_perc,
estd_overalloc_count
FROM V$PGA_TARGET_ADVICE;
==== Find the total PGA memory used by processes ====
select round(sum(pga_used_mem)/(1024*1024),2) pga_used_mb from v$process;
==== To calculate the amount of memory that you may need for PGA ====
select * from v$pgastat;
select * from v$pga_target_advice;
See [[https://docs.oracle.com/cd/E11882_01/server.112/e40402/dynviews_2096.htm]] for details on v$pgastat\\
See [[https://docs.oracle.com/en/database/oracle/oracle-database/12.2/refrn/V-PGA_TARGET_ADVICE.html]] for details on v$pga_target_advice\\
See [[https://dba010.com/2011/05/31/how-to-determine-if-pga-is-set-properly/]] for reference of below queries.
col name for a40
select b.name
, sum(a.value) value
from v$sysstat a
, v$statname b
where a.statistic# = b.statistic#
and b.name like '%workarea executions - %'
group by b.name
/
NAME VALUE
---------------------------------------- --------------------
workarea executions - onepass 1081618
workarea executions - multipass 34847
workarea executions - optimal 469688227
The goal is to get rid of all passes and have everything optimal.\\
One pass means that data has had to be swapped out to the temporary tablespace to get the job done. Multipass means data had to be swapped out several times to get the job done.\\
These numbers are very high.
col pga_size_gb for 99999
col estd_pga_cache_hit_percentage for 99999 head "ESTD_PGA_CACHE|HIT_PERCENTAGE"
col estd_overalloc_count for 9999999999 head "ESTD_OVER|ALLOC_COUNT"
select round(pga_target_for_estimate/1024/1024/1024) pga_size_gb
, estd_pga_cache_hit_percentage
, estd_overalloc_count
from v$pga_target_advice
/
ESTD_PGA_CACHE ESTD_OVER
PGA_SIZE_GB HIT_PERCENTAGE ALLOC_COUNT
----------- -------------- -----------
0 94 324950
1 94 324929
2 94 324870
2 94 324084
3 98 322445
4 98 319425
4 98 301580
5 98 272987
5 98 249429
6 98 244328
9 99 192640
12 99 122051
18 100 0
24 100 0
Setting the pga_aggregate_target to 18Gb will allow all processing to remain in the pga and not get swapped out to the temp tablespaces.
==== Check the table size and percentage of fragmentation ====
* [[https://orahow.com/how-to-find-and-remove-table-fragmentation-in-oracle-database/|How to Find and Remove Table Fragmentation in Oracle Database]]
select sum(bytes)/1024/1024/1024 from dba_segments where segment_name='&TABLE_NAME';
select table_name,avg_row_len,round(((blocks*16/1024)),2)||'MB' "TOTAL_SIZE",
round((num_rows*avg_row_len/1024/1024),2)||'Mb' "ACTUAL_SIZE",
round(((blocks*16/1024)-(num_rows*avg_row_len/1024/1024)),2) ||'MB' "FRAGMENTED_SPACE",
(round(((blocks*16/1024)-(num_rows*avg_row_len/1024/1024)),2)/round(((blocks*16/1024)),2))*100 "percentage"
from all_tables WHERE table_name='&TABLE_NAME';
==== Enable Automatic Memory Management (AMM) ====
AMM is enabled by setting one or both of the following memory parameters:
alter system set memory_max_target=2g scope=spfile;
alter system set memory_target=2g scope=spfile;
With these memory parameters set, AMM is enabled.\\
Memory will now be allocated automatically to where it is needed.\\
alter system set sga_target=0 scope=spfile;
alter system set pga_aggregate_target=0 scope=spfile;
If sga_target and/or pga_aggregate_target are set, these will be treated as minimum values.\\
If only one of sga_target or pga_aggregate_target is set, the other will be set to (memory_target - the value set).\\
=== Disable AMM ===
SQL> alter system reset memory_max_target scope=spfile sid='*';
SQL> alter system reset memory_target scope=spfile sid='*';
=== Enable ASMM ===
SQL> alter system set SGA_MAX_SIZE=1400m scope=spfile sid='*';
SQL> alter system set SGA_TARGET=1000m scope=spfile sid='*';
SQL> alter system set PGA_AGGREGATE_TARGET=480m scope=spfile sid='*';
=== Reboot database and verify that we have switched from AMM to ASMM ===
SQL> show parameter memory
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
memory_max_target big integer 0
memory_target big integer 0
--> AMM disabled
SQL> show parameter sga
NAME TYPE VALUE
------------------------ ----------- ------------------------------
sga_max_size big integer 1408M
sga_target big integer 912M
SQL> show parameter pga
NAME TYPE VALUE
------------------------ ----------- ------------------------------
pga_aggregate_target big integer 480M
--> ASMM enabled !
==== Show size of the large pool ====
select name, sum(bytes) from v$sgastat where upper(pool) = 'LARGE POOL' group by rollup (name);
==== Quick SGA sizing advice ====
The MMON background process gathers statistics about sga usage and updates the V$SGA_TARGET_ADVICE view.
--- DB_CACHE_ADVICE should be ON
SQL> show parameter db_cache_advice
NAME TYPE VALUE
------------------------------------ -------------------------------- ------------------
db_cache_advice string ON
-- STATISTICS_LEVEL should be TYPICAL/ALL.
SQL> show parameter statistics_level
NAME TYPE VALUE
------------------------------------ -------------------------------- --------------------------
statistics_level string TYPICAL
select sga_size
, sga_size_factor
, estd_physical_reads
, estd_db_time
from v$sga_target_advice
order by sga_size;
Note where the ESTD_PHYSICAL_READS drop
SGA_SIZE SGA_SIZE_FACTOR ESTD_PHYSICAL_READS ESTD_DB_TIME
---------- --------------- ------------------- ------------
3756 .375 2.0808E+10 11162201
5008 .5 2.0808E+10 11156419
6260 .625 2.0808E+10 11156419
7512 .75 2.0808E+10 11156419
8764 .875 2.0808E+10 11156419
10016 1 1.3837E+10 19275084
11268 1.125 7146720999 59698790
12520 1.25 5065662261 22754237
13772 1.375 4939747138 8321054
15024 1.5 4939747138 8319126
16276 1.625 4939747138 8319126
17528 1.75 4939747138 8319126
18780 1.875 4939747138 8319126
20032 2 4400110896 148965559
14 rows selected.
Suggestion would be to increase sga target by 1.25 as there is no longer a significant decrease in ESTD_PHYSICAL_READS for the increase in sga size.
==== SGA tuning ====
Problem with 12c SGA growing too high. Database keeps crashing due to memory issues. Started at 2G, then to 4G and now at 5G.\\
Raised SR with Oracle. This is the response
You need to query the advice views like V$MEMORY_TARGET_ADVICE, V$SGA_TARGET_ADVICE, V$SHARED_POOL_ADVICE etc.
Interpret the results and then make the changes to memory components as indicated by the SIZE column.
Please review
Note 1323708.1 : Tuning the SGA_TARGET using V$SGA_TARGET_ADVICE then follow the version specific advice.
Please note that Oracle recommend to specify a value for the each of the tunable parameters
i.e Shared Pool, Database Buffer Cache, Large Pool, Java Pool and Streams Pool even when AMM or ASMM is enabled (you are using AMM).
When minimum value for each of the tunable parameters is set, Oracle will make sure that the amount of memory being allocated for the corresponding pool will not shrink below the specified amount.
Best practices with auto-tuning are to include explicit, minimum settings for the various auto-tuned components.
This will help the auto-tuner make "smarter" choices about moving memory within the SGA.
While it is not required to set explicit settings, the auto-tuner can get over aggressive with memory moves when auto-tuned components are set to 0.
The parameter _kghdsidx_count controls the number of subpools used. Setting this parameter to 2 will be the best. Currently you have this parameter set to 5.
SQL> alter system set "_kghdsidx_count"=2 scope=spfile;
or add this in the pfile
"_kghdsidx_count"=2
As a best practice for SGA components you can use the following recommendations:
- SHARED_POOL_SIZE >= 2G (because minimum 1G/subpool is recommended)
- LARGE_POOL_SIZE >= 150M (used for parallel executions)
- STREAMS_POOL_SIZE >= 150M (if you use datapump regularly)
- JAVA_POOL_SIZE >= 150M (if you use java)
- SGA_TARGET >= 3G (because it should be greater by 10% of the sum of it's components)
or another one from an 11g incident...
ACTION PLAN
===========
1. We can see that your shared pool is divided intro 4 subpools.
Set _kghdsidx_count to 2 in order to be sure the shared pool will be divided only in 2 subpools and not more. You currently have 4 subpools which favor fragmentation.
connect / as sysdba
SQL > alter system set "_kghdsidx_count"=2 scope=spfile;
- restart the database
FYI: Starting with Oracle 9i the shared_pool will be divided into multiple sub-heaps. Until 9.0, the shared pool was always allocated in one large heap rather than multiple subheaps. The number of subpools even if produced a better performance, also it
could produce ora-4031 errors when there is not space in the subpool as a result of fragmentation. One process will use only a specific subpool and if an error is reported, it wont be migrated to other subpool. Oracle 9i implemented multiple subpools to avoid shared pool latch contention. But, the cost of the multiple pools is that the size of each subpool will be smaller and hence more susceptible to an ORA-4031. So, the parameter _kghdsidx_count can be used to override the default for the number of sub pools.
2. Decrease the number of open_cursors from 3000 to 1000.
The open_cursors parameter is defined per session. Having many cursors open per session is too much and it means that the cursors are not correctly handled/closed at application level.
1000 cursors created per sessions should be enough for any application. We recommend in some cases to go as low as 600 which should still be enough.
3. Apply the workaround to disable the use of durations by setting "_enable_shared_pool_durations=FALSE".
This will allow unpinned SQLA, KGLH0, and KGLHD memory to be freed to make room for new permanent allocations.
4. Set a minimum for the SGA within the memory_target size using the parameter sga_target. For example set sga_target=13G. This will mean that at all times 13G of memory from memory_target will be reserved for the SGA. More memory can be allocated to it if necessary and available.
So please modify accordingly the parameters sga_max_size and sga_target. This will require a database restart.
But.. From 1323708.1 ...
In Oracle11g (or higher), the information in the V$SGA_TARGET_ADVICE view is similar to that provided in the V$MEMORY_TARGET_ADVICE view for Automatic Shared Memory Management.
If MEMORY_TARGET is set, then SGA_TARGET should be set to 0. See Document 443746.1 for more details on this.
If MEMORY_TARGET is not set, use the same steps as for 10g.
==== Redo log file size and Database Performance ====
* [[https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:9540730000346298496]]
See how much time is spent writing redo logs and checkpointing
select /*+ ordered */
a.sid,
decode(a.type, 'BACKGROUND', substr (a.program,instr(a.program,'(',1,1)), 'FOREGROUND') type,
b.time_waited,
round(b.time_waited/b.total_waits,4) average_wait,
round((sysdate - a.logon_time)*24) hours_connected
from v$session_event b, v$session a
where a.sid = b.sid
and b.event = 'control file parallel write'
order by type, time_waited;
==== How much redo was generated / How many archivelog switches have occurred per hour over the past week? ====
set lines 200 pages 100
col day for a9 hea "Date\Hour"
col "00" for a5
col "01" for a5
col "02" for a5
col "03" for a5
col "04" for a5
col "05" for a5
col "06" for a5
col "07" for a5
col "08" for a5
col "09" for a5
col "10" for a5
col "11" for a5
col "12" for a5
col "13" for a5
col "14" for a5
col "15" for a5
col "16" for a5
col "17" for a5
col "18" for a5
col "19" for a5
col "20" for a5
col "21" for a5
col "22" for a5
col "23" for a5
col "all" for a9 heading "All day"
alter session set nls_date_format='DD-MON-YY'
/
select * from (
select trunc(first_time) day,
to_char(sum(decode(to_char(first_time,'HH24'),'00',1,0)),'9999') "00",
to_char(sum(decode(to_char(first_time,'HH24'),'01',1,0)),'9999') "01",
to_char(sum(decode(to_char(first_time,'HH24'),'02',1,0)),'9999') "02",
to_char(sum(decode(to_char(first_time,'HH24'),'03',1,0)),'9999') "03",
to_char(sum(decode(to_char(first_time,'HH24'),'04',1,0)),'9999') "04",
to_char(sum(decode(to_char(first_time,'HH24'),'05',1,0)),'9999') "05",
to_char(sum(decode(to_char(first_time,'HH24'),'06',1,0)),'9999') "06",
to_char(sum(decode(to_char(first_time,'HH24'),'07',1,0)),'9999') "07",
to_char(sum(decode(to_char(first_time,'HH24'),'08',1,0)),'9999') "08",
to_char(sum(decode(to_char(first_time,'HH24'),'09',1,0)),'9999') "09",
to_char(sum(decode(to_char(first_time,'HH24'),'10',1,0)),'9999') "10",
to_char(sum(decode(to_char(first_time,'HH24'),'11',1,0)),'9999') "11",
to_char(sum(decode(to_char(first_time,'HH24'),'12',1,0)),'9999') "12",
to_char(sum(decode(to_char(first_time,'HH24'),'13',1,0)),'9999') "13",
to_char(sum(decode(to_char(first_time,'HH24'),'14',1,0)),'9999') "14",
to_char(sum(decode(to_char(first_time,'HH24'),'15',1,0)),'9999') "15",
to_char(sum(decode(to_char(first_time,'HH24'),'16',1,0)),'9999') "16",
to_char(sum(decode(to_char(first_time,'HH24'),'17',1,0)),'9999') "17",
to_char(sum(decode(to_char(first_time,'HH24'),'18',1,0)),'9999') "18",
to_char(sum(decode(to_char(first_time,'HH24'),'19',1,0)),'9999') "19",
to_char(sum(decode(to_char(first_time,'HH24'),'20',1,0)),'9999') "20",
to_char(sum(decode(to_char(first_time,'HH24'),'21',1,0)),'9999') "21",
to_char(sum(decode(to_char(first_time,'HH24'),'22',1,0)),'9999') "22",
to_char(sum(decode(to_char(first_time,'HH24'),'23',1,0)),'9999') "23",
to_char(count(to_char(first_time,'DD')),'9999') "all"
from v$log_history
group by trunc(first_time)
order by trunc(first_time) desc
)
where rownum < 8
order by 1
/
set lines 80
==== How much archive (redo volume) has been generated per day? ====
Also how much has RMAN deleted
set lines 1000 pages 100
col day for a15 head "Date"
select sum_arch.day
, round(sum_arch.generated_gb,1) generated_gb
, round(sum_arch_del.archived_gb,1) archived_gb
, round((sum_arch.generated_gb - sum_arch_del.archived_gb),1) remaining_gb
from (
select to_char (completion_time, 'dd-mm-yyyy') day
, sum (round ( (blocks * block_size) / (1024 * 1024 * 1024), 2)) generated_gb
from v$archived_log
where archived = 'YES'
group by to_char (completion_time, 'dd-mm-yyyy')) sum_arch
, (
select to_char (completion_time, 'dd-mm-yyyy') day
, sum (round ( (blocks * block_size) / (1024 * 1024 * 1024), 2)) archived_gb
from v$archived_log
where archived = 'YES' and deleted = 'YES'
group by to_char (completion_time, 'dd-mm-yyyy')) sum_arch_del
where sum_arch.day = sum_arch_del.day(+)
order by to_date (day, 'dd-mm-yyyy') desc
/
set lines 80
==== Top session activity ====
* [[https://support.oracle.com/epmos/faces/DocumentDisplay?id=232443.1|How to Identify Resource Intensive SQL ("TOP SQL") (Doc ID 232443.1)]]
Enter READS, EXECS or CPU to order session activity by that column
set lines 500 pages 1000 verif off
col username for a15
col machine for a26
col module for a30
col logon_time for a20
col program for a30
col killer for a12
col osuser for a10
prompt Enter CPU, READS or EXECS
prompt (Press Enter for CPU default)
select nvl(a.username, '(oracle)') as username
, a.osuser
, a.sid||','||a.serial# killer
, c.value as &&TYPE
, a.lockwait
, a.status
, a.module
, a.machine
, a.program
, to_char(a.logon_time,'dd-mon-yyyy hh24:mi:ss') as logon_time
from v$session a
, v$sesstat c
, v$statname d
where 1=1
and a.sid = c.sid
and c.statistic# = d.statistic#
and d.name = decode(upper('&TYPE'), 'READS', 'session logical reads',
'EXECS', 'execute count',
'CPU', 'CPU used by this session',
'CPU used by this session'
)
order by c.value desc
/
undef TYPE
* [[https://www.funoracleapps.com/2019/10/query-to-check-session-details-in.html|A session collecting query from funoracleapps.com]]
select s.ecid
, s.inst_id
, s.sid
, s.serial#
, p.spid
, s.status
, s.machine
, s.action
, s.module
, s.terminal
, s.sql_id
, s.last_call_et
, s.event
, s.client_info
, s.plsql_subprogram_id
, s.program
, s.client_identifier
, ( select max( substr( sql_text , 1, 40 )) FROM gv$sql sq WHERE sq.sql_id = s.sql_id ) sql_text
, ( select object_name FROM dba_procedures WHERE object_id = plsql_entry_object_id AND subprogram_id = 0) plsql_entry_object
, ( select procedure_name FROM dba_procedures WHERE object_id = plsql_entry_object_id AND subprogram_id = plsql_entry_subprogram_id) plsql_entry_subprogram
, ( select object_name FROM dba_procedures WHERE object_id = plsql_object_id AND subprogram_id = 0) plsql_entry_object
, ( select procedure_name FROM dba_procedures WHERE object_id = plsql_object_id AND subprogram_id = PLSQL_SUBPROGRAM_ID) plsql_entry_subprogram
, 'alter system kill session ' || '''' || s.SID || ',' || s.serial# ||',@'|| s.inst_id||''''|| ' immediate;' kill_session
from gv$session s
, gv$process p
where
--client_identifier like '%HIMANSHU.SINGH%'
--s.ecid like '%ZnHWOPoUDWbG%'
-- sid=4361
--p.spid='1196'
--s.program like '%ICM%'
and p.addr=s.paddr
and p.inst_id = s.inst_id
/
==== Show current used undo blocks for ongoing transactions ====
select vs.sid
, vs.serial#
, vs.username
, vs.program
, vt.used_ublk
, vt.used_urec
from v$session vs
, v$transaction vt
where vs.taddr = vt.addr
order by 5 desc, 6 desc
==== Pinpoint which sessions are using lots of undo ====
select a.sid
, b.name
, a.value
from v$sesstat a
, v$statname b
where a.statistic# = b.statistic#
and a.statistic# = 176 # undo change vector size
order by a.value desc
==== How many blocks have been changed by sessions? ====
High values indicate a session generating lots of redo\\
Use this query to check for programs generating lots of redo when these programs activate more than one transaction.
select vs.sid
, vs.serial#
, vs.username
, vs.program
, vi.block_changes
from v$session vs
, v$sess_io vi
where vs.sid = vi.sid
order by 5 desc
, 1, 2, 3, 4;
==== Top SQL ====
Shows the SQL statements that have caused the most disk reads per execution since the instance was last started
set lines 1000 pages 1000
set verif off
col sql_text for a150
select *
from (
select substr(a.sql_text,1,200) sql_text
, trunc(a.disk_reads/decode(a.executions,0,1,a.executions)) reads_per_execution
, a.buffer_gets
, a.disk_reads
, a.executions
, a.sorts
, a.address
from v$sqlarea a
order by 2 desc
)
where rownum <= 11
/
set lines 80
Top ten SQL statements with the greatest aggregate elapsed time
set lines 1000 pages 1000
col sql_text for a150
SELECT sql_id,child_number,sql_text, elapsed_time
FROM (SELECT sql_id, child_number, sql_text, elapsed_time,
cpu_time,disk_reads,
RANK () OVER (ORDER BY elapsed_time DESC) AS elapsed_rank
FROM v$sql)
WHERE elapsed_rank <= 10
/
set lines 80
See the explain plan of these SQL's by feeding the sql_id and child_no into this cracker!
SELECT * FROM TABLE (DBMS_XPLAN.display_cursor (&sql_id, &child_no,'TYPICAL -BYTES'));
==== Top waits ====
Displays a list of the events currently being waited on by active sessions.\\
The meaning of the wait_time and seconds_in_wait columns varies depending on their values follows:\\
* wait_time - A non-zero value represents the session’s last wait time, while a zero value indicates that the session is currently waiting.\\
* seconds_in_wait - When the wait_time is zero, the seconds_in_wait value represents the seconds spent in the current wait condition.\\
When the wait_time is greater than zero, the seconds_in_wait value represents the seconds since the start of the last wait,\\
and (seconds_in_wait - wait_time / 100) is the active seconds since the last wait ended.
set lines 200 pages 1000
col username for a20
col event for a30
col wait_class for a15
select nvl(s.username, '(oracle)') as username
, s.sid
, s.serial#
, sw.event
, sw.wait_class
, sw.wait_time
, sw.seconds_in_wait
, sw.state
from v$session_wait sw
, v$session s
where 1=1
and s.sid = sw.sid
order by sw.seconds_in_wait desc
/
and with the SQL...
select a.sid
, a.event
, a.wait_time
, round(c.physical_read_bytes/1024/1024/1024,2) gb_read
, round(c.physical_write_bytes/1024/1024/1024,2) gb_write
, c.sql_text
from v$session_wait a
, v$session b
, v$sql c
where 1=1
and a.sid = b.sid
and b.sql_id = c.sql_id
order by wait_time desc
/
==== Session wait history ====
Once a session of interest has been identified, we can display the history of events associated with that session
set lines 200 pages 1000
set verif off
col username for a20
col event for a40
select nvl(s.username, '(oracle)') as username
, s.sid
, s.serial#
, se.event
, se.total_waits
, se.total_timeouts
, se.time_waited
, se.average_wait
, se.max_wait
, round(se.time_waited_micro/1000000,2) waited_secs
from v$session_event se
, v$session s
where 1=1
and s.sid = se.sid
and s.sid = &1
order by se.time_waited desc
/
==== System waits ====
select event
, total_waits
, total_timeouts
, time_waited
, average_wait
, time_waited_micro
from v$system_event
order by event
/
==== ASH queries ====
SELECT NVL(a.event, 'ON CPU') AS event,
COUNT(*) AS total_wait_time
FROM v$active_session_history a
WHERE a.sample_time > SYSDATE - 5/(24*60) -- 5 mins
GROUP BY a.event
ORDER BY total_wait_time DESC;
and
SELECT NVL(a.event, 'ON CPU') AS event,
COUNT(*)*10 AS total_wait_time
FROM dba_hist_active_sess_history a
WHERE a.sample_time > SYSDATE - 1
GROUP BY a.event
ORDER BY total_wait_time DESC;
==== Oracle Log File Sync Wait Event ====
Reference: [[http://logicalread.solarwinds.com/oracle-log-file-sync-wait-event-dr01/|logicalread.solarwinds.com]]\\
Snippet:
When a user session waits on the 'log file sync' event, it is actually waiting for the LGWR process to write the log buffer to the redo log file and\\
return confirmation/control back to it. If the total wait time is significant, review the average wait time. If the average wait time is low but the\\
number of waits is high, reduce the number of commits by batching (or committing after 'n') rows.
If slow I/O, investigate the following:
# Reduce contention on existing disks.\\
# Put log files on faster disks.\\
# Put alternate redo logs on different disks to minimise the effect archive processes (log files switches).\\
# Review application design, use NOLOGGING operations where appropriate, and avoid changing more data than required.\\
If wait times are still significant, review each component of the 'log file sync' and tune separately.
==== Shared Memory Problem (unable to allocate shared memory ...) - and how to avoid it using bind variables ====
* [[https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::p11_question_id:528893984337|use bind variables - asktom]]\\
Just to give you a tiny idea of how huge of a difference this can make performance wise, you only need to run a very small test:
tkyte@TKYTE816> alter system flush shared_pool;
System altered.
tkyte@TKYTE816> declare
2 type rc is ref cursor;
3 l_rc rc;
4 l_dummy all_objects.object_name%type;
5 l_start number default dbms_utility.get_time;
6 begin
7 for i in 1 .. 1000
8 loop
9 open l_rc for
10 'select object_name
11 from all_objects
12 where object_id = ' || i;
13 fetch l_rc into l_dummy;
14 close l_rc;
15 end loop;
16 dbms_output.put_line
17 ( round( (dbms_utility.get_time-l_start)/100, 2 ) ||
18 ' seconds...' );
19 end;
20 /
14.86 seconds...
PL/SQL procedure successfully completed.
tkyte@TKYTE816> declare
2 type rc is ref cursor;
3 l_rc rc;
4 l_dummy all_objects.object_name%type;
5 l_start number default dbms_utility.get_time;
6 begin
7 for i in 1 .. 1000
8 loop
9 open l_rc for
10 'select object_name
11 from all_objects
12 where object_id = :x'
13 using i;
14 fetch l_rc into l_dummy;
15 close l_rc;
16 end loop;
17 dbms_output.put_line
18 ( round( (dbms_utility.get_time-l_start)/100, 2 ) ||
19 ' seconds...' );
20 end;
21 /
1.27 seconds...
PL/SQL procedure successfully completed.
That is pretty dramatic. The fact is that not only does this execute much faster (we spent more time PARSING our queries then actually EXECUTING them!) it will let more users use your system simultaneously.
==== EXPLAIN PLAN ====
=== Usage (old school) ===
If no access to the system plan_table, create your own (also to keep the plans longer than a session), run $ORACLE_HOME/rdbms/admin/utlxplan.sql
explain plan
[[set statement_id = 'statement_id']]
[[into table_name ]]
for sql_statement
=== See the results ===
select rtrim(lpad(' ', 2*level) || rtrim(operation) || ' ' || rtrim(options) || ' ' || object_name) query_plan
, cost
, cardinality
from plan_table
connect by prior id = parent_id
start with id = 0
=== Usage (new school) ===
1. Explain plan for the most recent SQL statement executed in the session
set pages 0
select * from table(dbms_xplan.display_cursor);
2. Execute an explain plan command on a SELECT statement
explain plan for
select *
from emp e
, dept d
where d.deptno = e.deptno
and e.ename = 'benoit'
/
set pages 0 lines 150
select * from table(dbms_xplan.display);
3. Explain plan on a previously executed statement\\
Find the SQL_ID\\
select sql_id, child_number
from v$sql
where sql_text like '%%';
Get the explain_plan
select * from table(dbms_xplan.display_cursor(('&sql_id',&child_number));
==== Virtual Indexes ====
An index created to see if the optimiser would use it without actually having to build it
SQL> ALTER SESSION SET "_use_nosegment_indexes"=TRUE;
Session altered.
SQL> CREATE INDEX sh.sales_vi1 ON sh.sales(quantity_sold) NOSEGMENT;
Index created.
Now re-run the explain plan and see the difference.
==== Statspack ====
If you are using Standard Edition, you cannot use the Grid utilities or to debug performance issues. You need to use the "old" method.\\
[[http://www.akadia.com/services/ora_statspack_survival_guide.html|http://www.akadia.com/services/ora_statspack_survival_guide.html]]\\
Reproduced here in case the page disappears...
Overview
STATSPACK is a performance diagnosis tool, available since Oracle8i. STATSPACK can be considered BSTAT/ESTAT's successor, incorporating many new features. STATSPACK is a diagnosis tool for instance-wide performance problems; it also supports application tuning activities by providing data which identifies high-load SQL statements. STATSPACK can be used both proactively to monitor the changing load on a system, and also reactively to investigate a performance problem.
Remember to set timed_statistics to true for your instance. Setting this parameter provides timing data which is invaluable for performance tuning.
The «more is better» approach is not always better!
The single most common misuse of STATSPACK is the «more is better» approach. Often STATSPACK reports spans hours or even days. The times between the snapshots (the collection points) should, in general, be measured in minutes, not hours and never days.
The STATSPACK reports we like are from 1 5-minute intervals during a busy or peak time, when the performance is at its worst. That provides a very focused look at what was going wrong at that exact moment in time. The problem with a very large STATSPACK snapshot window, where the time between the two snapshots is measured in hours, is that the events that caused serious performance issues for 20 minutes during peak processing don't look so bad when they're spread out over an 8-hour window. It's also true with STATSPACK that measuring things over too long of a period tends to level them out over time. Nothing will stand out and strike you as being wrong. So, when taking snapshots, schedule them about 15 to 30 minutes (maximum) apart. You might wait 3 or 4 hours between these two observations, but you should always do them in pairs and within minutes of each other.
«Having a history of the good times is just as important as having a history of the bad; you need both»
Another common mistake with STATSPACK is to gather snapshots only when there is a problem. That is fine to a point, but how much better would it be to have a STATSPACK report from when things were going good to compare it with when things are bad. A simple STATSPACK report that shows a tremendous increase in physical 1/0 activity or table scans (long tables) could help you track down that missing index. Or, if you see your soft parse percentage value went from 99% to 70%, you know that someone introduced a new feature into the system that isn't using bind variables (and is killing you). Having a history of the good times is just as important as having a history of the bad; you need both.
Architecture
To fully understand the STATSPACK architecture, we have to look at the basic nature of the STATSPACK utility. The STATSPACK utility is an outgrowth of the Oracle UTLBSTAT and UTLESTAT utilities, which have been used with Oracle since the very earliest versions.
UTLBSTAT - UTLESTAT
The BSTAT-ESTAT utilities capture information directly from the Oracle's in-memory structures and then compare the information from two snapshots in order to produce an elapsed-time report showing the activity of the database. If we look inside utlbstat.sql and utlestat.sql, we see the SQL that samples directly from the view: V$SYSSTAT;
insert into stats$begin_stats select * from v$sysstat;
insert into stats$end_stats select * from v$sysstat;
STATSPACK
When a snapshot is executed, the STATSPACK software will sample from the RAM in-memory structures inside the SGA and transfer the values into the corresponding STATSPACK tables. These values are then available for comparing with other snapshots.
Note that in most cases, there is a direct correspondence between the v$ view in the SGA and the corresponding STATSPACK table. For example, we see that the stats$sysstat table is similar to the v$sysstat view.
SQL> desc v$sysstat;
Name Null? Type
----------------------------------------- -------- -----------------------
STATISTIC# NUMBER
NAME VARCHAR2(64)
CLASS NUMBER
VALUE NUMBER
STAT_ID NUMBER
SQL> desc stats$sysstat;
Name Null? Type
----------------------------------------- -------- -----------------------
SNAP_ID NOT NULL NUMBER
DBID NOT NULL NUMBER
INSTANCE_NUMBER NOT NULL NUMBER
STATISTIC# NOT NULL NUMBER
NAME NOT NULL VARCHAR2(64)
VALUE NUMBER
It is critical to your understanding of the STATSPACK utility that you realize the information captured by a STATSPACK snapshot is accumulated values. The information from the V$VIEWS collects database information at startup time and continues to add the values until the instance is shutdown. In order to get a meaningful elapsed-time report, you must run a STATSPACK report that compares two snapshots as shown above. It is critical to understand that a report will be invalid if the database is shut down between snapshots. This is because all of the accumulated values will be reset, causing the second snapshot to have smaller values than the first snapshot.
Installing and Configuring STATSPACK
Create PERFSTAT Tablespace
The STATSPACK utility requires an isolated tablespace to obtain all of the objects and data. For uniformity, it is suggested that the tablespace be called PERFSTAT, the same name as the schema owner for the STATSPACK tables. It is important to closely watch the STATSPACK data to ensure that the stats$sql_summary table is not taking an inordinate amount of space.
SQL> CREATE TABLESPACE perfstat
DATAFILE '/u01/oracle/db/AKI1_perfstat.dbf' SIZE 1000M REUSE
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 512K
SEGMENT SPACE MANAGEMENT AUTO
PERMANENT
ONLINE;
Run the Create Scripts
Now that the tablespace exists, we can begin the installation process of the STATSPACK software. Note that you must have performed the following before attempting to install STATSPACK.
Run catdbsyn.sql as SYS
Run dbmspool.sql as SYS
$ cd $ORACLE_HOME/rdbms/admin
$ sqlplus "/ as sysdba"
SQL> start spcreate.sql
Choose the PERFSTAT user's password
-----------------------------------
Not specifying a password will result in the installation FAILING
Enter value for perfstat_password: perfstat
Choose the Default tablespace for the PERFSTAT user
---------------------------------------------------
Below is the list of online tablespaces in this database which can
store user data. Specifying the SYSTEM tablespace for the user's
default tablespace will result in the installation FAILING, as
using SYSTEM for performance data is not supported.
Choose the PERFSTAT users's default tablespace. This is the tablespace
in which the STATSPACK tables and indexes will be created.
TABLESPACE_NAME CONTENTS STATSPACK DEFAULT TABLESPACE
------------------------------ --------- ----------------------------
PERFSTAT PERMANENT
SYSAUX PERMANENT *
USERS PERMANENT
Pressing will result in STATSPACK's recommended default
tablespace (identified by *) being used.
Enter value for default_tablespace: PERFSTAT
Choose the Temporary tablespace for the PERFSTAT user
-----------------------------------------------------
Below is the list of online tablespaces in this database which can
store temporary data (e.g. for sort workareas). Specifying the SYSTEM
tablespace for the user's temporary tablespace will result in the
installation FAILING, as using SYSTEM for workareas is not supported.
Choose the PERFSTAT user's Temporary tablespace.
TABLESPACE_NAME CONTENTS DB DEFAULT TEMP TABLESPACE
------------------------------ --------- --------------------------
TEMP TEMPORARY *
Pressing will result in the database's default Temporary
tablespace (identified by *) being used.
Enter value for temporary_tablespace: TEMP
.....
.....
Creating Package STATSPACK...
Package created.
No errors.
Creating Package Body STATSPACK...
Package body created.
No errors.
NOTE:
SPCPKG complete. Please check spcpkg.lis for any errors.
Check the Logfiles: spcpkg.lis, spctab.lis, spcusr.lis
Adjusting the STATSPACK Collection Level
STATSPACK has two types of collection options, level and threshold. The level parameter controls the type of data collected from Oracle, while the threshold parameter acts as a filter for the collection of SQL statements into the stats$sql_summary table.
SQL> SELECT * FROM stats$level_description ORDER BY snap_level;
Level 0 \tThis level captures general statistics, including rollback segment, row cache, SGA, system events, background events, session events, system statistics, wait statistics, lock statistics, and Latch information.
Level 5 \tThis level includes capturing high resource usage SQL Statements, along with all data captured by lower levels.
Level 6 \tThis level includes capturing SQL plan and SQL plan usage information for high resource usage SQL Statements, along with all data captured by lower levels.
Level 7 \tThis level captures segment level statistics, including logical and physical reads, row lock, itl and buffer busy waits, along with all data captured by lower levels.
Level 10 \tThis level includes capturing Child Latch statistics, along with all data captured by lower levels.
You can change the default level of a snapshot with the statspack.snap function. The i_modify_parameter => 'true' changes the level permanent for all snapshots in the future.
SQL> exec statspack.snap(i_snap_level => 6, i_modify_parameter => 'true');
Create, View and Delete Snapshots
sqlplus perfstat/perfstat
SQL> exec statspack.snap;
SQL> select name,snap_id,to_char(snap_time,'DD.MM.YYYY:HH24:MI:SS')
"Date/Time" from stats$snapshot,v$database;
NAME SNAP_ID Date/Time
--------- ---------- -------------------
AKI1 4 14.11.2004:10:56:01
AKI1 1 13.11.2004:08:48:47
AKI1 2 13.11.2004:09:00:01
AKI1 3 13.11.2004:09:01:48
SQL> @?/rdbms/admin/sppurge;
Enter the Lower and Upper Snapshot ID
Create the Report
sqlplus perfstat/perfstat
SQL> @?/rdbms/admin/spreport.sql
Statspack at a Glance
What if you have this long STATSPACK report and you want to figure out if everything is running smoothly? Here, we will review what we look for in the report, section by section. We will use an actual STATSPACK report from our own Oracle 10g system.
Statspack Report Header
STATSPACK report for
DB Name DB Id Instance Inst Num Release RAC Host
------------ ----------- ------------ -------- ----------- --- ----------------
AKI1 2006521736 AKI1 1 10.1.0.2.0 NO akira
Snap Id Snap Time Sessions Curs/Sess Comment
--------- ------------------ -------- --------- -------------------
Begin Snap: 5 14-Nov-04 11:18:00 15 14.3
End Snap: 6 14-Nov-04 11:33:00 15 10.2
Elapsed: 15.00 (mins)
Cache Sizes (end)
~~~~~~~~~~~~~~~~~
Buffer Cache: 24M Std Block Size: 4K
Shared Pool Size: 764M Log Buffer: 1,000K
Note that this section may appear slightly different depending on your version of Oracle. For example, the Curs/Sess column, which shows the number of open cursors per session, is new with Oracle9i (an 8i Statspack report would not show this data).
Here, the item we are most interested in is the elapsed time. We want that to be large enough to be meaningful, but small enough to be relevant (15 to 30 minutes is OK). If we use longer times, we begin to lose the needle in the haystack.
Statspack Load Profile
Load Profile
~~~~~~~~~~~~ Per Second Per Transaction
--------------- ---------------
Redo size: 425,649.84 16,600,343.64
Logical reads: 1,679.69 65,508.00
Block changes: 2,546.17 99,300.45
Physical reads: 77.81 3,034.55
Physical writes: 78.35 3,055.64
User calls: 0.24 9.55
Parses: 2.90 113.00
Hard parses: 0.16 6.27
Sorts: 0.76 29.82
Logons: 0.01 0.36
Executes: 4.55 177.64
Transactions: 0.03
% Blocks changed per Read: 151.59 Recursive Call %: 99.56
Rollback per transaction %: 0.00 Rows per Sort: 65.61
Here, we are interested in a variety of things, but if we are looking at a "health check", three items are important:
The Hard parses (we want very few of them)
Executes (how many statements we are executing per second / transaction)
Transactions (how many transactions per second we process).
This gives an overall view of the load on the server. In this case, we are looking at a very good hard parse number and a fairly light system load (1 - 4 transactions per second is low).
Statspack Instance Efficiency Percentage
Next, we move onto the Instance Efficiency Percentages section, which includes perhaps the only ratios we look at in any detail:
Instance Efficiency Percentages (Target 100%)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Buffer Nowait %: 100.00 Redo NoWait %: 99.99
Buffer Hit %: 95.39 In-memory Sort %: 100.00
Library Hit %: 99.42 Soft Parse %: 94.45
Execute to Parse %: 36.39 Latch Hit %: 100.00
Parse CPU to Parse Elapsd %: 59.15 % Non-Parse CPU: 99.31
Shared Pool Statistics Begin End
------ ------
Memory Usage %: 10.28 10.45
% SQL with executions>1: 70.10 71.08
% Memory for SQL w/exec>1: 44.52 44.70
The three in bold are the most important: Library Hit, Soft Parse % and Execute to Parse. All of these have to do with how well the shared pool is being utilized. Time after time, we find this to be the area of greatest payback, where we can achieve some real gains in performance.
Here, in this report, we are quite pleased with the Library Hit and the Soft Parse % values. If the library Hit ratio was low, it could be indicative of a shared pool that is too small, or just as likely, that the system did not make correct use of bind variables in the application. It would be an indicator to look at issues such as those.
OLTP System
The Soft Parse % value is one of the most important (if not the only important) ratio in the database. For a typical OLTP system, it should be as near to 100% as possible. You quite simply do not hard parse after the database has been up for a while in your typical transactional / general-purpose database. The way you achieve that is with bind variables. In a regular system like this, we are doing many executions per second, and hard parsing is something to be avoided.
Data Warehouse
In a data warehouse, we would like to generally see the Soft Parse ratio lower. We don't necessarily want to use bind variables in a data warehouse. This is because they typically use materialized views, histograms, and other things that are easily thwarted by bind variables. In a data warehouse, we may have many seconds between executions, so hard parsing is not evil; in fact, it is good in those environments.
The moral of this is ...
... to look at these ratios and look at how the system operates. Then, using that knowledge, determine if the ratio is okay given the conditions. If we just said that the execute-to-parse ratio for your system should be 95% or better, that would be unachievable in many web-based systems. If you have a routine that will be executed many times to generate a page, you should definitely parse once per page and execute it over and over, closing the cursor if necessary before your connection is returned to the connection pool.
Statspack Top 5 Timed Events
Moving on, we get to the Top 5 Timed Events section (in Oracle9i Release 2 and later) or Top 5 Wait Events (in Oracle9i Release 1 and earlier).
Top 5 Timed Events
~~~~~~~~~~~~~~~~~~ % Total
Event Waits Time (s) Call Time
-------------------------------------------- ------------ ----------- ---------
CPU time 122 91.65
db file sequential read 1,571 2 1.61
db file scattered read 1,174 2 1.59
log file sequential read 342 2 1.39
control file parallel write 450 2 1.39
-------------------------------------------------------------
Wait Events DB/Inst: AKI1/AKI1 Snaps: 5-6
-> s - second
-> cs - centisecond - 100th of a second
-> ms - millisecond - 1000th of a second
-> us - microsecond - 1000000th of a second
-> ordered by wait time desc, waits desc (idle events last)
This section is among the most important and relevant sections in the Statspack report. Here is where you find out what events (typically wait events) are consuming the most time. In Oracle9i Release 2, this section is renamed and includes a new event: CPU time.
CPU time is not really a wait event (hence, the new name), but rather the sum of the CPU used by this session, or the amount of CPU time used during the snapshot window. In a heavily loaded system, if the CPU time event is the biggest event, that could point to some CPU-intensive processing (for example, forcing the use of an index when a full scan should have been used), which could be the cause of the bottleneck.
Db file sequential read - This wait event will be generated while waiting for writes to TEMP space generally (direct loads, Parallel DML (PDML) such as parallel updates. You may tune the PGA AGGREGATE TARGET parameter to reduce waits on sequential reads.
Db file scattered read - Next is the db file scattered read wait value. That generally happens during a full scan of a table. You can use the Statspack report to help identify the query in question and fix it.
SQL ordered by Gets
Here you will find the most CPU-Time consuming SQL statements
SQL ordered by Gets DB/Inst: AKI1/AKI1 Snaps: 5-6
-> Resources reported for PL/SQL code includes the resources used by all SQL
statements called by the code.
-> End Buffer Gets Threshold: 10000 Total Buffer Gets: 720,588
-> Captured SQL accounts for 3.1% of Total Buffer Gets
-> SQL reported below exceeded 1.0% of Total Buffer Gets
CPU Elapsd Old
Buffer Gets Executions Gets per Exec %Total Time (s) Time (s) Hash Value
--------------- ------------ -------------- ------ -------- --------- ----------
16,926 1 16,926.0 2.3 2.36 3.46 1279400914
Module: SQL*Plus
create table test as select * from all_objects
Tablespace IO Stats
Tablespace
------------------------------
Av Av Av Av Buffer Av Buf
Reads Reads/s Rd(ms) Blks/Rd Writes Writes/s Waits Wt(ms)
-------------- ------- ------ ------- ------------ -------- ---------- ------
TAB 1,643 4 1.0 19.2 16,811 39 0 0.0
UNDO 166 0 0.5 1.0 5,948 14 0 0.0
SYSTEM 813 2 2.5 1.6 167 0 0 0.0
STATSPACK 146 0 0.3 1.1 277 1 0 0.0
SYSAUX 18 0 0.0 1.0 29 0 0 0.0
IDX 18 0 0.0 1.0 18 0 0 0.0
USER 18 0 0.0 1.0 18 0 0 0.0
-------------------------------------------------------------
Rollback Segment Stats
->A high value for "Pct Waits" suggests more rollback segments may be required
->RBS stats may not be accurate between begin and end snaps when using Auto Undo
managment, as RBS may be dynamically created and dropped as needed
Trans Table Pct Undo Bytes
RBS No Gets Waits Written Wraps Shrinks Extends
------ -------------- ------- --------------- -------- -------- --------
0 8.0 0.00 0 0 0 0
1 3,923.0 0.00 14,812,586 15 0 14
2 5,092.0 0.00 19,408,996 19 0 19
3 295.0 0.00 586,760 1 0 0
4 1,312.0 0.00 4,986,920 5 0 5
5 9.0 0.00 0 0 0 0
6 9.0 0.00 0 0 0 0
7 9.0 0.00 0 0 0 0
8 9.0 0.00 0 0 0 0
9 9.0 0.00 0 0 0 0
10 9.0 0.00 0 0 0 0
-------------------------------------------------------------
Rollback Segment Storage
->Optimal Size should be larger than Avg Active
RBS No Segment Size Avg Active Optimal Size Maximum Size
------ --------------- --------------- --------------- ---------------
0 364,544 0 364,544
1 17,952,768 8,343,482 17,952,768
2 25,292,800 11,854,857 25,292,800
3 4,321,280 617,292 6,418,432
4 8,515,584 1,566,623 8,515,584
5 126,976 0 126,976
6 126,976 0 126,976
7 126,976 0 126,976
8 126,976 0 126,976
9 126,976 0 126,976
10 126,976 0 126,976
-------------------------------------------------------------
Generate Execution Plan for given SQL statement
If you have identified one or more problematic SQL statement, you may want to check the execution plan. Remember the "Old Hash Value" from the report above (1279400914), then execute the scrip to generate the execution plan.
sqlplus perfstat/perfstat
SQL> @?/rdbms/admin/sprepsql.sql
Enter the Hash Value, in this example: 1279400914
SQL Text
~~~~~~~~
create table test as select * from all_objects
Known Optimizer Plan(s) for this Old Hash Value
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Shows all known Optimizer Plans for this database instance, and the Snap Id's
they were first found in the shared pool. A Plan Hash Value will appear
multiple times if the cost has changed
-> ordered by Snap Id
First First Plan
Snap Id Snap Time Hash Value Cost
--------- --------------- ------------ ----------
6 14 Nov 04 11:26 1386862634 52
Plans in shared pool between Begin and End Snap Ids
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Shows the Execution Plans found in the shared pool between the begin and end
snapshots specified. The values for Rows, Bytes and Cost shown below are those
which existed at the time the first-ever snapshot captured this plan - these
values often change over time, and so may not be indicative of current values
-> Rows indicates Cardinality, PHV is Plan Hash Value
-> ordered by Plan Hash Value
--------------------------------------------------------------------------------
| Operation | PHV/Object Name | Rows | Bytes| Cost |
--------------------------------------------------------------------------------
|CREATE TABLE STATEMENT |----- 1386862634 ----| | | 52 |
|LOAD AS SELECT | | | | |
| VIEW | | 1K| 216K| 44 |
| FILTER | | | | |
| HASH JOIN | | 1K| 151K| 38 |
| TABLE ACCESS FULL |USER$ | 29 | 464 | 2 |
| TABLE ACCESS FULL |OBJ$ | 3K| 249K| 35 |
| TABLE ACCESS BY INDEX ROWID |IND$ | 1 | 7 | 2 |
| INDEX UNIQUE SCAN |I_IND1 | 1 | | 1 |
| NESTED LOOPS | | 5 | 115 | 16 |
| INDEX RANGE SCAN |I_OBJAUTH1 | 1 | 10 | 2 |
| FIXED TABLE FULL |X$KZSRO | 5 | 65 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| FIXED TABLE FULL |X$KZSPR | 1 | 26 | 14 |
| VIEW | | 1 | 13 | 2 |
| FAST DUAL | | 1 | | 2 |
--------------------------------------------------------------------------------
Resolving Your Wait Events
The following are 10 of the most common causes for wait events, along with explanations and potential solutions:
1. DB File Scattered Read
This generally indicates waits related to full table scans. As full table scans are pulled into memory, they rarely fall into contiguous buffers but instead are scattered throughout the buffer cache. A large number here indicates that your table may have missing or suppressed indexes. Although it may be more efficient in your situation to perform a full table scan than an index scan, check to ensure that full table scans are necessary when you see these waits. Try to cache small tables to avoid reading them in over and over again, since a full table scan is put at the cold end of the LRU (Least Recently Used) list.
2. DB File Sequential Read
This event generally indicates a single block read (an index read, for example). A large number of waits here could indicate poor joining orders of tables, or unselective indexing. It is normal for this number to be large for a high-transaction, well-tuned system, but it can indicate problems in some circumstances. You should correlate this wait statistic with other known issues within the Statspack report, such as inefficient SQL. Check to ensure that index scans are necessary, and check join orders for multiple table joins. The DB_CACHE_SIZE will also be a determining factor in how often these waits show up. Problematic hash-area joins should show up in the PGA memory, but they're also memory hogs that could cause high wait numbers for sequential reads. They can also show up as direct path read/write waits.
3. Free Buffer
This indicates your system is waiting for a buffer in memory, because none is currently available. Waits in this category may indicate that you need to increase the DB_BUFFER_CACHE, if all your SQL is tuned. Free buffer waits could also indicate that unselective SQL is causing data to flood the buffer cache with index blocks, leaving none for this particular statement that is waiting for the system to process. This normally indicates that there is a substantial amount of DML (insert/update/delete) being done and that the Database Writer (DBWR) is not writing quickly enough; the buffer cache could be full of multiple versions of the same buffer, causing great inefficiency. To address this, you may want to consider accelerating incremental checkpointing, using more DBWR processes, or increasing the number of physical disks.
4. Buffer Busy
This is a wait for a buffer that is being used in an unshareable way or is being read into the buffer cache. Buffer busy waits should not be greater than 1 percent. Check the Buffer Wait Statistics section (or V$WAITSTAT) to find out if the wait is on a segment header. If this is the case, increase the freelist groups or increase the pctused to pctfree gap. If the wait is on an undo header, you can address this by adding rollback segments; if it's on an undo block, you need to reduce the data density on the table driving this consistent read or increase the DB_CACHE_SIZE. If the wait is on a data block, you can move data to another block to avoid this hot block, increase the freelists on the table, or use Locally Managed Tablespaces (LMTs). If it's on an index block, you should rebuild the index, partition the index, or use a reverse key index. To prevent buffer busy waits related to data blocks, you can also use a smaller block size: fewer records fall within a single block in this case, so it's not as "hot." When a DML (insert/update/ delete) occurs, Oracle Database writes information into the block, including all users who are "interested" in the state of the block (Interested Transaction List, ITL). To decrease waits in this area, you can increase the initrans, which will create the space in the block to allow multiple ITL slots. You can also increase the pctfree on the table where this block exists (this writes the ITL information up to the number specified by maxtrans, when there are not enough slots built with the initrans that is specified).
5. Latch Free
Latches are low-level queuing mechanisms (they're accurately referred to as mutual exclusion mechanisms) used to protect shared memory structures in the system global area (SGA). Latches are like locks on memory that are very quickly obtained and released. Latches are used to prevent concurrent access to a shared memory structure. If the latch is not available, a latch free miss is recorded. Most latch problems are related to the failure to use bind variables (library cache latch), redo generation issues (redo allocation latch), buffer cache contention issues (cache buffers LRU chain), and hot blocks in the buffer cache (cache buffers chain). There are also latch waits related to bugs; check MetaLink for bug reports if you suspect this is the case. When latch miss ratios are greater than 0.5 percent, you should investigate the issue.
6. Enqueue
An enqueue is a lock that protects a shared resource. Locks protect shared resources, such as data in a record, to prevent two people from updating the same data at the same time. An enqueue includes a queuing mechanism, which is FIFO (first in, first out). Note that Oracle's latching mechanism is not FIFO. Enqueue waits usually point to the ST enqueue, the HW enqueue, the TX4 enqueue, and the TM enqueue. The ST enqueue is used for space management and allocation for dictionary-managed tablespaces. Use LMTs, or try to preallocate extents or at least make the next extent larger for problematic dictionary-managed tablespaces. HW enqueues are used with the high-water mark of a segment; manually allocating the extents can circumvent this wait. TX4s are the most common enqueue waits. TX4 enqueue waits are usually the result of one of three issues. The first issue is duplicates in a unique index; you need to commit/rollback to free the enqueue. The second is multiple updates to the same bitmap index fragment. Since a single bitmap fragment may contain multiple rowids, you need to issue a commit or rollback to free the enqueue when multiple users are trying to update the same fragment. The third and most likely issue is when multiple users are updating the same block. If there are no free ITL slots, a block-level lock could occur. You can easily avoid this scenario by increasing the initrans and/or maxtrans to allow multiple ITL slots and/or by increasing the pctfree on the table. Finally, TM enqueues occur during DML to prevent DDL to the affected object. If you have foreign keys, be sure to index them to avoid this general locking issue.
7. Log Buffer Space
This wait occurs because you are writing the log buffer faster than LGWR can write it to the redo logs, or because log switches are too slow. To address this problem, increase the size of the log files, or increase the size of the log buffer, or get faster disks to write to. You might even consider using solid-state disks, for their high speed.
8. Log File Switch
All commit requests are waiting for "logfile switch (archiving needed)" or "logfile switch (Checkpoint. Incomplete)." Ensure that the archive disk is not full or slow. DBWR may be too slow because of I/O. You may need to add more or larger redo logs, and you may potentially need to add database writers if the DBWR is the problem.
9. Log File Sync
When a user commits or rolls back data, the LGWR flushes the session's redo from the log buffer to the redo logs. The log file sync process must wait for this to successfully complete. To reduce wait events here, try to commit more records (try to commit a batch of 50 instead of one at a time, for example). Put redo logs on a faster disk, or alternate redo logs on different physical disks, to reduce the archiving effect on LGWR. Don't use RAID 5, since it is very slow for applications that write a lot; potentially consider using file system direct I/O or raw devices, which are very fast at writing information.
10. Idle Event.
There are several idle wait events listed after the output; you can ignore them. Idle events are generally listed at the bottom of each section and include such things as SQL*Net message to/from client and other background-related timings. Idle events are listed in the stats$idle_event table.
Remove STATSPACK from the Database
After a STATSPACK session you want to remove the STATSPACK tables.
sqlplus "/ as sysdba"
SQL> @?/rdbms/admin/spdrop.sql
SQL> DROP TABLESPACE perfstat INCLUDING CONTENTS AND DATAFILES;
=== References ===
* [[http://www.dba-oracle.com/plsql/t_plsql_v$.htm|http://www.dba-oracle.com/plsql/t_plsql_v$.htm]]
==== Help with Oracle Trace File Analyser (TFA) ====
find current running sqls
Find active sessions in oracle database
Find waitevents in database
Find sessions generating undo
Find the temp usage of the sessions
Find sessions generating lot of redo
Monitor tablespace usage
Script to Monitor undo tablespace usage
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10053 OPTIMIZER TRACE
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* [[https://www.linkedin.com/pulse/19-great-things-you-can-do-vactivesessionhistory-part-merav-kedem|19 Great Things You Can Do With V$ACTIVE_SESSION_HISTORY (Part 1)]]
* [[https://blogs.oracle.com/connect/post/beginning-performance-tuning-trace-your-steps|How to trace SQL sessions to identify Oracle Database bottlenecks - Arup Nanda]]
* [[https://support.oracle.com/epmos/faces/DocumentDisplay?id=33089.1|TROUBLESHOOTING: Possible Causes of Poor SQL Performance (Doc ID 33089.1)]]
* [[https://docs.oracle.com/database/121/TGSQL/tgsql_histo.htm#TGSQL95033|Histograms - Database SQL Tuning Guide - oracle.com]]
* [[https://www.informit.com/articles/article.aspx?p=1400612&seqNum=5|Oracle Performance Tuning: A Methodical Approach - informit.com]]