SQL TUNING 101

Copyright © 2016 Accenture All rights reserved. | 2
Alex Zaballa
http://alexzaballa.blogspot.com/
@alexzaballa
https://www.linkedin.com/in/alexzaballa
275 and counting…

Worked for 3 years in Brazil as a Clipper/Delphi Developer (15 years old)
1997-1999
Worked for 7 years in Brazil as an Oracle Developer
2000 - 2007
Worked for 8 years in Angola as an Oracle DBA
for the Ministry of Finance.
2007 - 2015

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SQL TUNING 101
Before start….

ORACLE DATABASE MULTILINGUAL ENGINE – BETA 12.2
Initial beta with JavaScript Stored Procedures
http://www.oracle.com/technetwork/database/multiling
ual-engine/overview/index.html

http://www.oracle.com/technetwork/pt/articles/database-
performance/odb-12-2-multilingual-4394909-ptb.html

https://livesql.oracle.com

OVERVIEW
Database Tuning
Vs
SQL Tuning

OVERVIEW
Developers
vs
SQL

TOM KYTE

SQL TUNING 101
Let’s begin….

SQL TUNING 101
The application is running slow today!
Nothing has changed!

YES, SOMETHING HAS CHANGED
• Database upgraded
• Statistics gathered (automatic?)
• Schema changed
• Database parameter changed
• Application changed
• Operating system (OS) and hardware changed
• Data volume changed
• More active users

HOW TO START TROUBLESHOOTING?
One SQL?
All the database?
ASH and AWR
**Requires Oracle Diagnostics Pack

SQL TUNING
Proactive

SQL TUNING
Reactive

PROACTIVE – TOOLS

EDB360 - TOP SQLS

EDB360 - TOP EVENTS

EDB360
DEMO

AWR REPORT
• 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

AWR REPORT
DEMO

REACTIVE - TOOLS

SQLT (SQLTXPLAIN) DIAGNOSTIC TOOL
(DOC ID 215187.1)
• Pros: Supported by Oracle
• Cons: Requires Installation

SQLT (SQLTXPLAIN) DIAGNOSTIC TOOL
(DOC ID 215187.1)

SQLD360
• Pros: No Installation
• Cons: Might miss some information
under rare circumstances

SQLTXPLAIN VS SQLD360
https://mauro-pagano.com/2017/04/29/sqltxplain-vs-sqld360-differences-and-similarities/

SQLD360 – HOW TO USE
• Download the free tool:
https://github.com/mauropagano/sqld360/
• Execution:
SQL> sqld360.sql <sql_id> [N|D|T]

SQLD360

SQLD360
DEMO

SQLD360
If you want to know more:
https://mauro-pagano.com/category/sqld360/

EXPLAIN PLAN
How about Explain Plan?

EXPLAIN PLAN
Explain Plain lies!

EXPLAIN PLAN
It does not actually execute the SQL statement.
Runtime factors can influence choice of plan:
• Dynamic Sampling
• Bind Variable Peeking
• Adaptive Features

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)

Copyright © 2016 Accenture All rights reserved. |
DBMS_XPLAN

DBMS_XPLAN
Display plan for the last SQL executed:
select * from table(dbms_xplan.display_cursor());

DBMS_XPLAN
Display plan for one specific SQL
• Get SQL_ID:

SQL_ID - 18C

DBMS_XPLAN
DEMO

DBMS_XPLAN
Child Number ?

DBMS_XPLAN
DEMO

Copyright © 2016 Accenture All rights reserved. |https://blogs.oracle.com/optimizer/entry/how_do_i_know_if
/*+ gather_plan_statistics */
or
Alter session set statistics_level = ALL
ESTIMATE VS ACTUAL

ESTIMATE VS ACTUAL
DEMO

SQL MONITOR
• Introduced in Oracle Database 11g.
• Automatically started when a SQL statement either runs
in parallel or has consumed at least 5 seconds of
combined CPU and I/O.
• Hint /*+ MONITOR */

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

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

SQL MONITOR

DEMO
SQL MONITOR

COST OF AN INDEX

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

• Not always good
• Not always bad
FULL TABLE SCAN

ANALYZING TABLES

ANALYZING TABLES
https://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_4005.htm

ROW-BY-ROW PROCESSING
https://blog.jooq.org/2018/04/19/the-performance-difference-between-sql-row-by-row-updating-batch-updating-and-bulk-updating/

ROW-BY-ROW

PL/SQL FORALL

ONE UPDATE

EVENT 10053

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

EVENT 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)

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

EVENT 10053
11G R1
ALTER SESSION SET EVENTS
'trace[rdbms.SQL_Optimizer.*][sql:my_sql_id]';
ALTER SESSION SET EVENTS
'trace[rdbms.SQL_Optimizer.*] off';

EVENT 10053
11G R2 – 18c
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.

EVENT 10053
ALTER SESSION SET EVENTS '10053 trace name
context forever, level 1';
SELECT * FROM tb_master p
WHERE EXISTS (SELECT 1 FROM tb_detail f
WHERE f.id_master=p.id);
context off';

EVENT 10053
QUERY BLOCK – 2 parts

EVENT 10053
Parallelism - Disabled

EVENT 10053
Subtitles

EVENT 10053
Database Parameters

EVENT 10053
System Statistics

EVENT 10053
No statistics for these tables

EVENT 10053
Dynamic Sampling

EVENT 10053
Full Table Scan – No Index

EVENT 10053
Original: Final:
Final Query

EVENT 10053
Final Plan

EVENT 10053
Example 2

EVENT 10053 Let’s run this one

EVENT 10053
Original:
Final:

Query Transformations
EVENT 10053

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

SUBQUERY UNNESTING
Original:
SELECT * FROM accounts
WHERE custno IN
(SELECT custno FROM customers);
Changed:
SELECT accounts.*
FROM accounts, customers
WHERE accounts.custno = customers.custno;

VIEW MERGING
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;
Changed:
SELECT empno
FROM emp
WHERE deptno = 10 AND empno > 7800;

PREDICATE PUSHING
Original:
CREATE VIEW two_emp_tables AS
FROM emp1
UNION
FROM emp2;
SELECT ename FROM two_emp_tables
WHERE deptno = 20;

PREDICATE PUSHING
Changed:
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
Original:
SELECT *
FROM emp, dept
WHERE emp.deptno = 20
AND emp.deptno = dept.deptno;
Changed:
SELECT *
FROM emp, dept
WHERE emp.deptno = 20
AND emp.deptno = dept.deptno
AND dept.deptno = 20;

COUNT(1) VS COUNT(*)
What is the difference between count(1) and count(*) ?

Nothing

MORE ABOUT THE EVENT 10053

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 12.1 this 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.
ADAPTIVE FEATURES

https://blogs.oracle.com/optimizer/entry/improvement_of_auto_sampling_statistics_gathering_feature_in_oracle_database_11g
estimate_percent => dbms_stats.auto_sample_size
STATISTICS

Should I use?
HINTS

Query running on M7: 180 Minutes
Query after db clone  P8+Storage ?
• Time: 29 hours
Query running on M7 after SQL tuning: 17 minutes
SQL TUNING ON EXADATA

SQL TUNING ON EXADATA

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 your queries.
PENDING STATISTICS

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

Check the retention:
select DBMS_STATS.GET_STATS_HISTORY_RETENTION from dual;
Default is 31 days.
RESTORE STATISTICS FROM HISTORY

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;

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;
EXPORT AND IMPORT SCHEMA STATISTICS

Incremental statistics for partitioned tables:
dbms_stats.set_table_prefs(null,'SALES','INCREMENTAL','TRUE')
INCREMENTAL STATISTICS

INCREMENTAL STATISTICS

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;
INVISIBLE INDEXES

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);
SQL TRACE, 10046, TRCSESS AND 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;

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);

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);

ALTER SESSION SET TRACEFILE_IDENTIFIER = "MY_TRC_FILE";

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

12.2
v$diag_trace_file
v$diag_trace_file_contents

EVENT 10046

context forever, level 12';
SELECT * FROM tb_pai p
WHERE EXISTS (SELECT 1 FROM tb_filho f
WHERE f.id_pai=p.id);
context off';
EVENT 10046

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

SQL TRACE, 10046, TRCSESS AND
TKPROF

SQLCL
http://www.oracle.com/technetwork/developer-tools/sqlcl/downloads/index.html

QUESTIONS?

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

SQL TUNING 101

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