Oracle SQL Tuning

Oracle
SQL Tuning 101
Alex Zaballa, Accenture Enkitec Group

Alex Zaballa
http://alexzaballa.blogspot.com/
@alexzaballa
https://www.linkedin.com/in/alexzaballa
Worked for 3 years as a Clipper/Delphi Developer (15 years old)
Worked for 7 years in Brazil as an Oracle Developer.
Worked 8 years for the Ministry of Finance
In Angola as a DBA
March - 2007 until March - 2015*

Oracle Database
Enterprise Edition +
Diagnostics Pack +
Tuning Pack
*

Database Tuning
Vs
SQL Tuning
*

•Aplicações multi-banco
•ORM : Object Relational
Mapper

”The Oracle optimizer uses
the constraints to make
better decisions on join
paths.”

Cost of an Index
FKs **
In-Memory**
*

Nada mudou e hoje a
aplicação está lenta!

Mudanças que podem trazer
problemas
• Database upgraded
• Statistics gathered
• Schema changed
• Database parameter changed
• Application changed
• Operating system (OS) and hardware changed
• Data volume changed by more active users

Ferramentas para SQL Tuning -
Oracle
• SQL Trace (and TKPROF)
• Active Session History (ASH)
• EXPLAIN PLAN FOR
• AUTOTRACE
• SQL Developer
• DBMS_XPLAN
• SQL Monitor

ASH e AWR
• 1 sec snapshots of V$SESSION into ASH
• Every 10 ASH samples into AWR
**Requires Oracle Diagnostics Pack
*

AWR
• SQL ordered by Elapsed Time
• SQL ordered by CPU Time
• SQL ordered by User I/O Wait Time
• SQL ordered by Gets
• SQL ordered by Reads
• SQL ordered by Physical Reads (UnOptimized)
• SQL ordered by Executions
• SQL ordered by Parse Calls
• SQL ordered by Sharable Memory
• SQL ordered by Version Count
• SQL ordered by Cluster Wait Time*

SQL ordered by Executions - RAC

Reativo - SQLT Diagnostic Tool
(Doc ID 215187.1)
• Prós: Suportada e atualizada pela Oracle
• Contras: Necessário instalação
Criada pelo Carlos Sierra
*

Reativo - SQLD360
Criada pelo Mauro Pagano
*

Explain Plan
Apenas tenta prever o plano que será executado!

Explain Plan
• Bind Variable Peeking
• Adaptive Features
• Etc

Now what?
• DBMS_XPLAN.DISPLAY_CURSOR
• V$SQL_PLAN%

DBMS_XPLAN.DISPLAY_CURSOR
• SQL_ID
• CURSOR_CHILD_NO (default 0)
• FORMAT
 TYPICAL = DEFAULT
 ALL = TYPICAL + QB + PROJECTION + ALIAS + REMOTE
 ADVANCED = ALL + OUTLINE + BINDS
 ALLSTATS = IOSTATS + MEMSTATS (all executions)
 ALLSTATS LAST (last execution)
 ADAPTIVE (12c)

DBMS_XPLAN
• DISPLAY (from PLAN_TABLE)
• DISPLAY_CURSOR
• DISPLAY_AWR
• DISPLAY_SQL_PLAN_BASELINE
• DISPLAY_SQL_SET
SELECT * FROM
TABLE(DBMS_XPLAN.DISPLAY_CURSOR('sql_id',child,'ADVANCED'));

Estimate vs Actual
https://blogs.oracle.com/optimizer/entry/how_do_i_know_if
/*+ gather_plan_statistics */
or
Alter session set statistics_level = ALL

SQL MONITOR
• Real-time SQL monitoring foi introduzido no
Oracle Database 11g.
• Parallel queries, DML e DDL são
automaticamente monitorados.
• SQLs que consumem 5 segundos ou mais
segundos de CPU ou I/O em uma única
execução
• Hint /*+ MONITOR */

SQL MONITOR
• Oracle Enterprise Manager
• EM Database Express (12c)
• SQL Developer
• Linha de Comando
**Part of the Oracle Tuning Pack

SQL MONITOR
select dbms_sqltune.report_sql_monitor(
sql_id => 'gjabwvvr07w09',
report_level=>'ALL',
type => 'ACTIVE') from dual;

Evento 10053
Mais conhecido como ”Wolfganging”
” Wolfgang Breitling was the first guy to really
analyze the content of these 10053 trace files
and publish his findings.”
Wolfgang wrote a paper called “A Look
Under the Hood of CBO.”

Evento 10053
ALTER SESSION SET EVENTS '10053 trace name
context forever, level 1';
SELECT * FROM EMP WHERE ENAME = 'SCOTT';
context off';

Evento 10053
Level 1 or Level 2?
•1. Parameters used by the optimizer (level 1 only)
•2. Index statistics (level 1 only)
•3. Column statistics
•4. Single Access Paths
•5. Join Costs
•6. Table Joins Considered
•7. Join Methods Considered (NL/MS/HA)

Evento 10053
For another session:
SYS.DBMS_SYSTEM.SET_EV (SID,SERIAL ,10053,1)
Disable:
SYS.DBMS_SYSTEM.SET_EV (SID,SERIAL ,10053,0)

Evento 10053
11G R1 – SQL Inside PL/SQL
ALTER SESSION SET EVENTS
'trace[rdbms.SQL_Optimizer.*][sql:my_sql_id]';
ALTER SESSION SET EVENTS
'trace[rdbms.SQL_Optimizer.*] off';

Evento 10053
11G R2
dbms_sqldiag.dump_trace(
p_sql_id=>’92c3fw9svc3rc’,
p_child_number=>0,
p_component=>'Compiler',
p_file_id=>’MY_Trace_File');
** Doesn’t require you to re-execute the statement.

Evento 10053
SELECT * FROM tb_pai p
WHERE EXISTS (SELECT 1 FROM tb_filho f
WHERE f.id_pai=p.id);
context off';

Evento 10053
QUERY BLOCK – 2 partes da query

Evento 10053
Paralelismo desabilitado

Evento 10053
System Statistics

Evento 10053
Sem Estatísticas

Evento 10053
Table Scan – Sem Índices

OR Expansion
Query Original:
SELECT * FROM emp
WHERE job = 'CLERK' OR deptno = 10;
Query Transformada:
SELECT * FROM emp
WHERE job = 'CLERK’
UNION ALL
SELECT * FROM emp
WHERE deptno = 10 AND job <> 'CLERK';

Subquery Unnesting
Query Original:
SELECT * FROM accounts
WHERE custno IN
(SELECT custno FROM customers);
Query Transformada:
SELECT accounts.*
FROM accounts, customers
WHERE accounts.custno = customers.custno;

View Merging
Query Original:
CREATE VIEW emp_10 AS
SELECT empno, ename, job, sal, comm, deptno
FROM emp
WHERE deptno = 10;
SELECT empno FROM emp_10
WHERE empno > 7800;
Query transformada:
SELECT empno
FROM emp
WHERE deptno = 10 AND empno > 7800;

Predicate Pushing
Query Original:
CREATE VIEW two_emp_tables AS
FROM emp1
UNION
FROM emp2;
SELECT ename FROM two_emp_tables
WHERE deptno = 20;

Predicate Pushing
Query Transformada:
SELECT ename
FROM ( SELECT empno, ename, job,sal, comm, deptno
FROM emp1 WHERE deptno = 20
UNION
SELECT empno, ename, job,sal, comm, deptno
FROM emp2 WHERE deptno = 20 );

Transitivity
Query Original:
SELECT *
FROM emp, dept
WHERE emp.deptno = 20
AND emp.deptno = dept.deptno;
Query Transformada:
SELECT *
FROM emp, dept
WHERE emp.deptno = 20
AND emp.deptno = dept.deptno
AND dept.deptno = 20;

Full Table Scan
https://www.slideshare.net/MauroPagano3/
full-table-scan-friend-or-foe
*

Full Table Scan
https://www.slideshare.net/MauroPagano3/
full-table-scan-friend-or-foe

Full Table Scan
https://richardfoote.wordpress.com/2008/05/12/index-scan-
or-full-table-scan-the-magic-number-magic-dance/
*

Full Table Scan
• Clustering Factor --> How well ordered the rows in
the table are in relation to the index.
• Selectivity of the query
• Number of table blocks
• Effective multiblock read count
• Relative cost of single vs. multiblock I/Os
• Parallelism
• Etc

Adaptive Features
Oracle Database 12.1
•OPTIMIZER_ADAPTIVE_FEATURES
Default TRUE

Adaptive Features
Oracle Database 12.2 introduces the new
split-up adaptive parameters:
•OPTIMIZER_ADAPTIVE_PLANS
•OPTIMITER_ADAPTIVE_STATISTICS.

Adaptive Features
• On Oracle Database 12.1this can be
achieved by installing two patches.

Adaptive Features
The patch for bug# 22652097 introduces the two parameters
OPTIMIZER_ADAPTIVE_PLANS and
OPTIMIZER_ADAPTIVE_STATISTICS, and in addition removes
the parameter OPTIMIZER_ADAPTIVE_FEATURES.
The patch for bug# 21171382 disables the automatic creation
of extended statistics unless the optimizer preference
AUTO_STATS_EXTENSIONS is set to ON.

Statistics
https://blogs.oracle.com/optimizer/entry/improvement_of_auto_sampling_statistics
_gathering_feature_in_oracle_database_11g
estimate_percent => dbms_stats.auto_sample_size

Hints
• Devo utilizar ?
• O desenvolvedores/dbas sabem mais que
o otimizador?

Hints
• Use para fornecer dados ao otimizador
que as estatísticas falharam em informar;
• Use com precaução;
• Use como último recurso.

SQL Tuning on EXADATA
• Tempo da query na M7: 180 minutos
• Tempo após clone - P8+Storage ?
• Tempo após ajuste da query: 29 horas
• Tempos após ajuste no M7: 17 minutos

Pending Statistics
Set table preferences:
begin
dbms_stats.set_table_prefs (
ownname => 'SCOTT',
tabname => 'EMP',
pname => 'PUBLISH',
pvalue => 'FALSE'
);
end;
Collect the statistics.

Pending Statistics
select num_rows,
to_char(last_analyzed,'dd/mm/rrrr hh24:mi:ss')
from all_tab_pending_stats
where table_name = 'EMP';

Pending Statistics
alter session set
optimizer_use_pending_statistics = true;
Test the queries.

Pending Statistics
If it’s ok:
dbms_stats.publish_pending_stats('SCOTT',
'EMP');
or:
dbms_stats.delete_pending_stats(’SCOTT',
’EMP');

Restore Statistics from History
Check the retention:
select
DBMS_STATS.GET_STATS_HISTORY_RETENTI
ON from dual;
Default is 31 days.

Statistics available for the table:
SELECT OWNER,
TABLE_NAME,
STATS_UPDATE_TIME
FROM dba_tab_stats_history
WHERE table_name='MY_TABLE';

Begin
dbms_stats.restore_table_stats(
'SCOTT',
'EMP',
‘08-NOV-16 11.38.05.015640 AM +08:00’);
End;

Export and Import schema
statistics
begin
dbms_stats.CREATE_STAT_TABLE( ownname=>user
, stattab=>'MY_STATS_TABLE'
);
end;
begin
dbms_stats.export_schema_stats( ownname=>user
, statid=>'CURRENT_STATS'
);
End;

Export and Import schema
statistics
EXPDP / IMPDP
begin
dbms_stats.import_schema_stats( ownname=>user
, statid=>'CURRENT_STATS'
);
End;

Incremental Statistics
Estatísticas incrementais para Tabelas
Particionadas:
dbms_stats.set_table_prefs(null,'SALES'
,'INCREMENTAL','TRUE')
11g**

Invisible Indexes
• CREATE INDEX index_name ON
table_name(column_name) INVISIBLE;
• ALTER INDEX index_name INVISIBLE;
• ALTER INDEX index_name VISIBLE;

Invisible Indexes
ALTER SESSION SET
OPTIMIZER_USE_INVISIBLE_INDEXES=TRUE;

Row-by-Row Processing vs Bulk
Processing
Instead of fetching a single row at a time
it is possible to use the bulk features.

Processing

Processing
*

SQL trace, 10046, trcsess and
tkprof
ALTER SESSION SET sql_trace=TRUE;
ALTER SESSION SET sql_trace=FALSE;
EXEC DBMS_SESSION.set_sql_trace(sql_trace => TRUE);
EXEC DBMS_SESSION.set_sql_trace(sql_trace => FALSE);
ALTER SESSION SET EVENTS '10046 trace name context forever, level 12';
ALTER SESSION SET EVENTS '10046 trace name context off';
EXEC DBMS_SYSTEM.set_sql_trace_in_session(sid=>0000, serial#=>0000, sql_trace=>TRUE);
EXEC DBMS_SYSTEM.set_sql_trace_in_session(sid=>0000, serial#=>0000, sql_trace=>FALSE);

tkprof
CONN sys/password AS SYSDBA;
ORADEBUG SETMYPID;
ORADEBUG SETOSPID 0000;
ORADEBUG SETORAPID 000000;
ORADEBUG EVENT 10046 TRACE NAME CONTEXT FOREVER, LEVEL 12;
ORADEBUG EVENT 10046 TRACE NAME CONTEXT OFF;

tkprof
EXEC DBMS_SUPPORT.start_trace(waits=>TRUE, binds=>TRUE);
EXEC DBMS_SUPPORT.stop_trace;
EXEC DBMS_SUPPORT.start_trace_in_session(sid=>0000, serial=>000000,
waits=>TRUE, binds=>TRUE);
EXEC DBMS_SUPPORT.stop_trace_in_session(sid=>0000, serial=>000000);

tkprof
10g:
DBMS_MONITOR.session_trace_enable(waits=>TRUE, binds=>FALSE);
DBMS_MONITOR.session_trace_enable(session_id =>0000, serial_num=>000000,
waits=>TRUE, binds=>TRUE);
DBMS_MONITOR.client_id_trace_enable(client_id=>'my_client', waits=>TRUE,
binds=>TRUE);
DBMS_MONITOR.serv_mod_act_trace_enable(service_name=>'my_srv',
module_name=>'my_test', action_name=>'calculating', waits=>TRUE, binds=>TRUE);

tkprof
ALTER SESSION SET TRACEFILE_IDENTIFIER =
"MY_TRC_FILE";

tkprof
SELECT p.tracefile
FROM v$session s
JOIN v$process p
ON s.paddr = p.addr
WHERE s.sid = MY_SID;

tkprof
12.2
v$diag_trace_file
v$diag_trace_file_contents

Evento 10046
SELECT * FROM tb_pai p
WHERE EXISTS (SELECT 1 FROM tb_filho f
WHERE f.id_pai=p.id);
context off';

tkprof
• TKPROF
• TRCSESS
• Trace Analyzer TRCANLZR (TRCA)
• Method R Tools

tkprof

tkprof
http://www.oraclenerd.com/2011/02/sql-developer-mr-trace.html

Thank You
Slides Available: http://www.slideshare.net/

Oracle SQL Tuning

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