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Module 4 Database SQL Tuning

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  1. Module 4 Database SQL Tuning Section 3 Application Performance

  2. Explain Plan Basics • The Explain Plan Utility and the Execution Plan • Why Execution Plans Are Important • Execution Plan Format • Sample Execution Tree

  3. The Explain Plan Utility and the Execution Plan SQL Statement Explain Plan Utility Other Tools: OEM SQL Studio Precise SQL TRACE TKPROF, etc.. plan_table Explain Report Execution Plan

  4. Why is the Explain Plan Utility Important? • An execution plan shows how Oracle is going to process a statement. • This helps tune statements = Better Performance • Builds SQL tuning skills = $$$ • Builds Application tuning skills = $$$ • When used by developers early in the development cycle, can uncover data model, index, and performance issues before its too late!

  5. Explain Report SQL SELECT LPAD(' ',2*(LEVEL-1))||operation “OPERATION” ,options “OPTIONS” ,DECODE(TO_CHAR(id),'0','COST = ' || NVL(TO_CHAR(position),'n/a'), object_name)“OBJECT NAME” ,id ||'-'|| NVL(parent_id, 0)||'-'|| NVL(position, 0) “ORDER” ,SUBSTR(optimizer,1,6) “OPT” FROM plan_table START WITH id = 0 AND statement_id = 'X' CONNECT BY PRIOR id = parent_id AND statement_id = 'X';

  6. Execution Plan Example SELECT cust_no ,cust_address ,cust_last_name ,cust_first_name FROM customer WHERE cust_phone = '3035551234'; OPERATION OPTIONS OBJECT NAME ORDER OPT ----------------------- ------------ ----------------- ------- ----- SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS BY ROWID CUSTOMER 1-0-1 INDEX RANGE SCAN IX_CUST_PHONE 2-1-1

  7. Execution Tree Example 1 TABLE ACCESS BY ROWID ON CUSTOMER 2 INDEX RANGE SCAN ON IX_CUST_PHONE

  8. OPERATIONS • ROW OPERATION • SET OPERATION

  9. ROW OPERATION • EXECUTED ON ONE ROW AT A TIME. • THE USER CAN SEE THE FIRST RESULT BEFORE THE LAST ROW IS FETCHED.

  10. SET OPERATION • EXECUTED ON A RESULT SET OF ROWS. • THE USER CANNOT SEE THE FIRST RESULT UNTIL ALL ROWS ARE FETCHED AND PROCESSED.

  11. SQL OPERATIONS • AND-EQUAL: ROW OPERATION • CONCATENATION: ROW OPERATION • CONNECT BY: ROW OPERATION • COUNT: ROW OPERATION • COUNT STOPKEY: ROW OPERATION • FILTER: ROW OPERATION • FOR UPDATE: SET OPERATION • INDEX RANGE SCAN: ROW OPERATION

  12. SQL OPERATIONS • INDEX UNIQUE SCAN: ROW OPERATION • INTERSECTION: SET OPERATION • MERGE JOIN: SET OPERATION • MINUS: SET OPERATION • NESTED LOOPS: ROW OPERATION • OUTER JOIN: SET OPERATION OR ROW OPERATION • PROJECTION: ROW OPERATION • REMOTE: ROW OPERATION OR SET OPERATION • VIEW: SET OPERATION

  13. SQL OPERATIONS • SEQUENCE: ROW OPERATION • SORT AGGREGATE: SET OPERATION • SORT GROUP BY: SET OPERATION • SORT JOIN: SET OPERATION • SORT ORDER BY: SET OPERATION • SORT UNIQUE: SET OPERATION • TABLE ACCESS BY ROWID: ROW OPERATION • TABLE ACCESS FULL: ROW OPERATION • UNION: SET OPERATION

  14. ORACLE OPTIMIZER MODES RULE-BASED COST-BASED

  15. ORACLE HINTS (Some of them) • RULE • ALL_ROWS • FIRST_ROWS • AND-EQUAL • FULL • HASH • INDEX • INDEX_ASC • INDEX_DESC

  16. ORACLE HINTS Continued • NO_MERGE • ORDERED • ROWID • USE_HASH • USE_NL • USE_MERGE • USE_STAR

  17. RULE Rule hint tells the optimizer to use the rule-based optimization for the query. All other hints within the query will be ignored.

  18. All_ROWS All_Rows hint optimizes the query for the best throughput- that is, to minimize the time it takes for all rows returned by the query.

  19. FIRST_ROWS First_Rows hint optimizes the query for the shortest response time to return the first row from the query.

  20. AND-EQUAL And-Equal hint tells the optimizer to perform an And-Equal operation on the indexes listed within the hint.

  21. FULL Full hint will perform a Full table scan. This hint might be used, if one knows the index scan used by the query would be a poor choice given the data distribution.

  22. INDEX • If a single index is used in the hint, that index will be used. • If multiple indexes are used in the hint, the optimizer will choose which indexes to use. • If only table name is used in the hint, then the optimizer will choose an index or indexes to use for that table.

  23. INDEX-ASC This hint is same as the Index hint.

  24. INDEX_DESC INDEX_DESC hint tells the optimizer to scan an index in the descending order of the indexed values.

  25. NO_MERGE This hint is available as of Oracle 7.3, which tells the optimizer not to merge a view’s SQL syntax with the syntax of a query that uses the view.

  26. ORDERED This hint will influence the order in which the tables are joined.

  27. USE_NL This hint tells the optimizer to perform a nested loop join, using the specified table as the driving table in the join.

  28. USE-MERGE This hint tells the optimizer to use a merge join between specified tables.

  29. USE_STAR This hint is available as of Oracle 7.3, tells the optimizer to use a composite key/star query execution path when resolving a join. These hints are typically used in data warehousing applications, which have a master table with small detail tables.

  30. Access Path and Operation Examples • Data Model for Examples • Access Paths: • Table Access Full • Table Access By ROWID • Index Unique Scan • Index Range Scan • Operations: • And-Equal • Nested Loops

  31. Data Model For Examples CUSTOMER *cust_no cust_last_name cust_first_name cust_phone cust_address cust_zip ORDER_HDR *order_no order_status order_create_dt order_desc order_cust_no order_amt ux_customer ux_order_hdr ix_cust_phone ix_order_status ix_cust_zip ix_order_cust_no

  32. Access Path:Table Access Full SELECT cust_no ,cust_last_name ,cust_first_name ,cust_address FROM customer;

  33. Access Path:Table Access Full SELECT cust_no ,cust_last_name ,cust_first_name ,cust_address FROM customer; OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS FULL CUSTOMER 1-0-1

  34. Access Path:Table Access Full 1 TABLE ACCESS FULL ON CUSTOMER SELECT cust_no ,cust_last_name ,cust_first_name ,cust_address FROM customer; OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS FULL CUSTOMER 1-0-1

  35. Access Path:Table Access By ROWID SELECT cust_no ,cust_last_name ,cust_first_name ,cust_address FROM customer WHERE ROWID = CHARTOROWID( :host );

  36. Access Path:Table Access By ROWID SELECT cust_no ,cust_last_name ,cust_first_name ,cust_address FROM customer WHERE ROWID = CHARTOROWID( :host ); OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS BY ROWID CUSTOMER 1-0-1

  37. Access Path:Table Access By ROWID SELECT cust_no ,cust_last_name ,cust_first_name ,cust_address FROM customer WHERE ROWID = CHARTOROWID( :host ); OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS BY ROWID CUSTOMER 1-0-1 1 TABLE ACCESS BY ROWID ON CUSTOMER

  38. Access Path:Index Unique Scan SELECT cust_last_name ,cust_first_name ,cust_address FROM customer WHERE cust_no = :host;

  39. Access Path:Index Unique Scan SELECT cust_last_name ,cust_first_name ,cust_address FROM customer WHERE cust_no = :host; OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS BY ROWID CUSTOMER 1-0-1 INDEX UNIQUE SCAN UX_CUSTOMER 2-1-1

  40. Access Path:Index Unique Scan 1 TABLE ACCESS BY ROWID ON CUSTOMER SELECT cust_last_name ,cust_first_name ,cust_address FROM customer WHERE cust_no = :host; OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS BY ROWID CUSTOMER 1-0-1 INDEX UNIQUE SCAN UX_CUSTOMER 2-1-1 2 INDEX UNIQUE SCAN ON UX_CUSTOMER

  41. Access Path:Index Range Scan SELECT cust_last_name ,cust_first_name ,cust_address FROM customer WHERE cust_phone = '3035551234';

  42. Access Path:Index Range Scan SELECT cust_last_name ,cust_first_name ,cust_address FROM customer WHERE cust_phone = '3035551234'; OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS BY ROWID CUSTOMER 1-0-1 INDEX RANGE SCAN IX_CUST_PHONE 2-1-1

  43. Access Path:Index Range Scan 1 TABLE ACCESS BY ROWID ON CUSTOMER SELECT cust_last_name ,cust_first_name ,cust_address FROM customer WHERE cust_phone = '3035551234'; OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS BY ROWID CUSTOMER 1-0-1 INDEX RANGE SCAN IX_CUST_PHONE 2-1-1 2 INDEX RANGE SCAN ON IX_CUST_PHONE

  44. And-Equal Operation SELECT cust_no ,cust_last_name ,cust_first_name ,cust_address FROM customer WHERE cust_phone = :host1 AND cust_zip = :host2;

  45. And-Equal Operation SELECT cust_no ,cust_last_name ,cust_first_name ,cust_address FROM customer WHERE cust_phone = :host1 AND cust_zip = :host2; OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS BY ROWID CUSTOMER 1-0-1 AND-EQUAL 2-1-1 INDEX RANGE SCAN IX_CUST_PHONE 3-2-1 INDEX RANGE SCAN IX_CUST_ZIP 4-2-2

  46. And-Equal Operation 1 TABLE ACCESS BY ROWID ON CUSTOMER SELECT cust_no ,cust_last_name ,cust_first_name ,cust_address FROM customer WHERE cust_phone = :host1 AND cust_zip = :host2; OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE TABLE ACCESS BY ROWID CUSTOMER 1-0-1 AND-EQUAL 2-1-1 INDEX RANGE SCAN IX_CUST_PHONE 3-2-1 INDEX RANGE SCAN IX_CUST_ZIP 4-2-2 2 AND-EQUAL 3 INDEX RANGE SCAN ON IX_CUST_PHONE 4 INDEX RANGE SCAN ON IX_CUST_ZIP

  47. Nested Loop Operation SELECT a.cust_last_name ,a.cust_first_name ,a.cust_address ,b.order_desc ,b.order_create_dt FROM customer a ,order_hdr b WHERE cust_phone = :host1 AND b.order_cust_no = a.cust_no AND b.order_status = 'OPEN';

  48. Nested Loop Operation SELECT a.cust_last_name ,a.cust_first_name ,a.cust_address ,b.order_desc ,b.order_create_dt FROM customer a ,order_hdr b WHERE cust_phone = :host1 AND b.order_cust_no = a.cust_no AND b.order_status = 'OPEN'; OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE NESTED LOOPS 1-0-1 TABLE ACCESS BY ROWID ORDER_HDR 2-1-1 INDEX RANGE SCAN IX_ORDER_STATUS 3-2-1 TABLE ACCESS BY ROWID CUSTOMER 4-1-2 INDEX UNIQUE SCAN UX_CUSTOMER 5-4-1

  49. Nested Loop Operation 1 NESTED LOOPS SELECT a.cust_last_name ,a.cust_first_name ,a.cust_address ,b.order_desc ,b.order_create_dt FROM customer a ,order_hdr b WHERE cust_phone = :host1 AND b.order_cust_no = a.cust_no AND b.order_status = 'OPEN'; OPERATION OPTIONS OBJECT NAME ORDER OPT ------------------ ------------ -------------------- ------- ------ SELECT STATEMENT COST = n/a 0-0-0 RULE NESTED LOOPS 1-0-1 TABLE ACCESS BY ROWID ORDER_HDR 2-1-1 INDEX RANGE SCAN IX_ORDER_STATUS 3-2-1 TABLE ACCESS BY ROWID CUSTOMER 4-1-2 INDEX UNIQUE SCAN UX_CUSTOMER 5-4-1 2 TABLE ACCESS BY ROWID ON ORDER_HDR 4 TABLE ACCESS BY ROWID ON CUSTOMER 3 INDEX RANGE SCAN ON IX_ORDER_STATUS 5 INDEX UNIQUE SCAN ON UX_CUSTOMER

  50. Tuning Examples • Index Suppression • Table Order in FROM Clause

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