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Tuning Oracle SQL Tuning Oracle SQL The Basics of Efficient The Basics of Efficient SQL SQL Common Sense Indexing The Optimizer Making SQL Efficient Finding Problem Queries Oracle Enterprise Manager Wait Event Interface Wait Event Interface

Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

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Page 1: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Tuning Oracle SQLTuning Oracle SQL

• The Basics of Efficient SQLThe Basics of Efficient SQL• Common Sense Indexing• The Optimizer

– Making SQL Efficient

• Finding Problem Queries• Oracle Enterprise Manager

– Wait Event InterfaceWait Event Interface

Page 2: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• SELECTSELECT– FOR UPDATEFOR UPDATE

• Filtering– WHERE

• ORDER BY– often ignored by the Optimizer– depends on query and index complexity– may need ORDER BY using composite indexes

• GROUP BY

The Basics of Efficient SQLThe Basics of Efficient SQLSELECT ** FROM division;

SELECT division_id, name, city, state, country FROM division;

SELECT division_iddivision_id FROM division;

SELECT ** FROM division;

SELECT division_id, name, city, state, country FROM division;

SELECT division_iddivision_id FROM division;

Page 3: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• SELECT– FOR UPDATE

• Filtering– WHEREWHERE

• ORDER BY– often ignored by the Optimizer– depends on query and index complexity – may need ORDER BY using composite indexes

• GROUP BY

The Basics of Efficient SQLThe Basics of Efficient SQL

Avoid unintentional full table scansSELECT * FROM division WHERE country LIKE '%a%'LIKE '%a%';

Match indexes

Exact hits (equality)SELECT * FROM division WHERE division_id = 1WHERE division_id = 1;

Range scans / skip scans / full index scans

EXISTS (correlate) faster than IN

Biggest filters first

Full table scans can sometimes be faster

Avoid unintentional full table scansSELECT * FROM division WHERE country LIKE '%a%'LIKE '%a%';

Match indexes

Exact hits (equality)SELECT * FROM division WHERE division_id = 1WHERE division_id = 1;

Range scans / skip scans / full index scans

EXISTS (correlate) faster than IN

Biggest filters first

Full table scans can sometimes be faster

Page 4: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

The Basics of Efficient SQLThe Basics of Efficient SQLResorts on result after WHERE and GROUP BY

Don’t repeat sorting (ORDER BY often ignored)

by SELECT

SELECT division_id FROM division ORDER BY division_id;

by WHERE

SELECT * FROM division WHERE division_id < 10 ORDER BY division_id;

GROUP BY

SELECT state, COUNT(state) FROM division GROUP BY state ORDER BY state;

by DISTINCT

SELECT DISTINCT(state) FROM division ORDER BY state;

by indexes

SELECT division_id FROM division ORDER BY division_id;

Resorts on result after WHERE and GROUP BY

Don’t repeat sorting (ORDER BY often ignored)

by SELECT

SELECT division_id FROM division ORDER BY division_id;

by WHERE

SELECT * FROM division WHERE division_id < 10 ORDER BY division_id;

GROUP BY

SELECT state, COUNT(state) FROM division GROUP BY state ORDER BY state;

by DISTINCT

SELECT DISTINCT(state) FROM division ORDER BY state;

by indexes

SELECT division_id FROM division ORDER BY division_id;

• SELECT– FOR UPDATE

• Filtering– WHERE

• ORDER BYORDER BY– often ignored by the Optimizer– depends on query and index complexity– may need ORDER BY using composite indexes

• GROUP BY

Page 5: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• SELECT– FOR UPDATE

• Filtering– WHERE

• ORDER BYORDER BY– often ignored by the Optimizer– depends on query and index complexity– may need ORDER BY using composite indexes

• GROUP BY

The Basics of Efficient SQLThe Basics of Efficient SQLResorts on result after WHERE and GROUP BY

Don’t repeat sorting (ORDER BY often ignored)

by SELECT

SELECT division_iddivision_id FROM division ORDER BY division_id;

by WHERE

SELECT * FROM division WHERE division_id < 10division_id < 10 ORDER BY division_id;

GROUP BY

SELECT state, COUNT(state) FROM division GROUP GROUP BY stateBY state ORDER BY state;

by DISTINCT

SELECT DISTINCT(state)DISTINCT(state) FROM division ORDER BY state;

by indexes

SELECT division_iddivision_id FROM division ORDER BY division_id;

Resorts on result after WHERE and GROUP BY

Don’t repeat sorting (ORDER BY often ignored)

by SELECT

SELECT division_iddivision_id FROM division ORDER BY division_id;

by WHERE

SELECT * FROM division WHERE division_id < 10division_id < 10 ORDER BY division_id;

GROUP BY

SELECT state, COUNT(state) FROM division GROUP GROUP BY stateBY state ORDER BY state;

by DISTINCT

SELECT DISTINCT(state)DISTINCT(state) FROM division ORDER BY state;

by indexes

SELECT division_iddivision_id FROM division ORDER BY division_id;

Page 6: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

The Basics of Efficient SQLThe Basics of Efficient SQL

GROUP BY

SELECT state, COUNT(state) FROM division GROUP BY state ORDER BY state;

HAVING (filters aggregate)

SELECT state, COUNT(state) FROM division GROUP BY state HAVING COUNT(state) > 1;

use WHERE

SELECT state, COUNT(state) FROM division WHERE state = 'NY' GROUP BY state;

not HAVING

SELECT state, COUNT(state) FROM division GROUP BY state HAVING state = 'NY';

GROUP BY

SELECT state, COUNT(state) FROM division GROUP BY state ORDER BY state;

HAVING (filters aggregate)

SELECT state, COUNT(state) FROM division GROUP BY state HAVING COUNT(state) > 1;

use WHERE

SELECT state, COUNT(state) FROM division WHERE state = 'NY' GROUP BY state;

not HAVING

SELECT state, COUNT(state) FROM division GROUP BY state HAVING state = 'NY';

• SELECT– FOR UPDATE

• Filtering– WHERE

• ORDER BY– often ignored by the Optimizer– depends on query and index complexity – may need ORDER BY using composite indexes

• GROUP BYGROUP BY– Use WHERE not HAVINGUse WHERE not HAVING

Page 7: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• SELECT– FOR UPDATE

• Filtering– WHERE

• ORDER BY– often ignored by the Optimizer– depends on query and index complexity– may need ORDER BY using composite indexes

• GROUP BYGROUP BY– Use WHERE not HAVINGUse WHERE not HAVING

The Basics of Efficient SQLThe Basics of Efficient SQL

GROUP BY

SELECT state, COUNT(state) FROM division GROUP BY state ORDER BY state;

HAVING (filters aggregate)

SELECT state, COUNT(state) FROM division GROUP BY state HAVING COUNT(state) > 1HAVING COUNT(state) > 1;

use WHERE

SELECT state, COUNT(state) FROM division WHERE WHERE state = 'NY'state = 'NY' GROUP BY state;

not HAVING

SELECT state, COUNT(state) FROM division GROUP BY state HAVING state = 'NY'HAVING state = 'NY';

GROUP BY

SELECT state, COUNT(state) FROM division GROUP BY state ORDER BY state;

HAVING (filters aggregate)

SELECT state, COUNT(state) FROM division GROUP BY state HAVING COUNT(state) > 1HAVING COUNT(state) > 1;

use WHERE

SELECT state, COUNT(state) FROM division WHERE WHERE state = 'NY'state = 'NY' GROUP BY state;

not HAVING

SELECT state, COUNT(state) FROM division GROUP BY state HAVING state = 'NY'HAVING state = 'NY';

Page 8: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• FunctionsFunctions– conversionsconversions– miss indexes

– counteract with function based indexing

– avoid using– DECODE– CASE expressions– set operators (UNION)

• Use sequencesUse sequences• Use equality (=) or range scans (>)Use equality (=) or range scans (>)

– avoid negatives (!=, NOT)– avoid LIKE

The Basics of Efficient SQLThe Basics of Efficient SQL

Page 9: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

The Basics of Efficient SQLThe Basics of Efficient SQL

• JoinsJoins– avoid Cartesian Products– avoid anti joins– avoid outer joins– perhaps replace

– multiple table complex joins– with subquery semi joins and inline views

• Be careful with viewsBe careful with views

Page 10: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Common Sense IndexingCommon Sense Indexing

• Don’t always need indexesDon’t always need indexes– table with few columns– static data– small tables– appended tables (SQL*Loader)

• How to indexHow to index– single column surrogate sequences– don’t override PK and FKs– avoid nullable columns

Page 11: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Common Sense IndexingCommon Sense Indexing

• Read write indexingRead write indexing– BTree

• Often read onlyOften read only– Bitmaps– IOTs– Clusters

Page 12: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Common Sense IndexingCommon Sense Indexing

• Read write indexing– BTree

– function based– can help a lot– get out of control

– everybody wants one

– reverse key– surrogate keys– High insertion rates

– not DW

– Oracle RAC

Page 13: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Common Sense IndexingCommon Sense Indexing

• Often read onlyOften read only– Bitmaps

– can be much faster than BTreescan be much faster than BTrees– can deteriorate drastically over timecan deteriorate drastically over time

– twice as fast in my book– at a previous client

– 1 year of DML activity– 100s of times slower– problem was nobody knew why– and nobody wanted to change anything

Page 14: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Common Sense IndexingCommon Sense Indexing

• Often read onlyOften read only– IOTs

– small number of columns– small tables– heard good things in Oracle RAC– even highly active DML environments

Page 15: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• Is intelligent– better with simple queries

• Is usually correct• Nothing is set in stone• Verify SQL code efficiency

– use EXPLAIN PLANEXPLAIN PLAN– SET AUTOTRACE ON EXPLAINSET AUTOTRACE ON EXPLAIN– $ORACLE_HOME/rdbms/admin/utlxplan.sql$ORACLE_HOME/rdbms/admin/utlxplan.sql

The OptimizerThe Optimizer

Page 16: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• Everything cost based– rule based is redundant

• Maintain statisticsstatistics• Dynamic samplingDynamic sampling

– OPTIMIZER_DYNAMIC_SAMPLING

• Set TIMED_STATISTICS • HistogramsHistograms

– maintain as for statistics– use for unevenly distributed indexes

The OptimizerThe Optimizer

Page 17: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• TablesTables– full Table scans

– small static tables– reading most of the rows

– over 10% for the Optimizer

– reading deleted rows– parallel table scans

– sample table scans– retrieve only portion of table by blocks or %

– SELECT * FROM generalledger SAMPLE(0.001);

– ROWID scans

The OptimizerThe Optimizer

Page 18: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• IndexesIndexes– index unique scan– index range scan

– reverse order index range scan

– index skip scan– index full scan

– fast full index scan

– others (very specific)

The OptimizerThe Optimizer

Page 19: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• JoinsJoins– nested loop join

– most efficient– row sets both small– one large and one small row set– one sorted

– hash join– both large with little difference– temporary hash table generated

The OptimizerThe Optimizer

Page 20: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• More on joinsMore on joins– sort merge join

– inefficient– both rows sets sorted then merge sorted

– other join types– semi joins– bitmap joins– star queries – Cartesian joins– outer joins (nested, hash or sort merge)

The OptimizerThe Optimizer

Page 21: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

• Hints can change thingsHints can change things– influence the optimizer

• CURSOR_SHARING• configuration parameter

• FORCE (OLTP)• EXACT (DW)

• FIRST or ALL_ROWS• DYNAMIC_SAMPLING

– change table scans• FULL

The OptimizerThe Optimizer

Page 22: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

The OptimizerThe Optimizer

• More on hintsMore on hints– change index scans

• INDEX_ASC, INDEX_DESC• INDEX_FFS• INDEX_JOIN (join indexes)• INDEX_SS_ASC or INDEX_SS_DESC• NO_INDEX, NO_INDEX_FFS or NO_INDEX_SS

– change joins• can change join type and influence with

parameters

– parallel SQL

Page 23: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Finding Problem QueriesFinding Problem Queries

• EXPLAIN PLANEXPLAIN PLAN– SET AUTOTRACE ON EXPLAIN– $ORACLE_HOME/rdbms/admin/utlxplan.sql$ORACLE_HOME/rdbms/admin/utlxplan.sql

• SQL Trace and TKPROF

Page 24: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event Wait Event InterfaceInterface

Wait Event Wait Event InterfaceInterface

Finding Problem QueriesFinding Problem Queries• Performance views

• V$SQLAREA• executions• parsing• sorting• disk and buffer reads• fetching

• V$SQL• optimizer cost• CPU time• elapsed time

• Performance views• V$SQLAREA

• executions• parsing• sorting• disk and buffer reads• fetching

• V$SQL• optimizer cost• CPU time• elapsed time

Page 25: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event InterfaceWait Event Interface

Page 26: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event InterfaceWait Event Interface

Page 27: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event InterfaceWait Event Interface

Page 28: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event InterfaceWait Event Interface

Page 29: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event InterfaceWait Event Interface

Page 30: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event InterfaceWait Event Interface

Page 31: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event InterfaceWait Event Interface

Page 32: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Performance overview

Page 33: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Database health overview

Page 34: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Drilldown

Page 35: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

More drilldown

Page 36: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

TopSQL

Page 37: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

EXPLAIN PLAN

Page 38: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event InterfaceWait Event Interface

Page 39: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event InterfaceWait Event Interface

Page 40: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Wait Event InterfaceWait Event Interface

Page 41: Tuning Oracle SQL The Basics of Efficient SQLThe Basics of Efficient SQL Common Sense Indexing The Optimizer –Making SQL Efficient Finding Problem Queries

Use the help filesUse the HELP FILES in Use the HELP FILES in

Oracle Enterprise Oracle Enterprise ManagerManager

Use the HELP FILES in Use the HELP FILES in Oracle Enterprise Oracle Enterprise

ManagerManager