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SQL Tuning 基础概述01 - autotrace的设定
1.autotrace的设定
SQL> set autotraceUsage: SET AUTOT[RACE] {OFF | ON | TRACE[ONLY]} [EXP[LAIN]] [STAT[ISTICS]]
set autot on--打开autotrace,之后执行的sql,会显示sql执行结果、执行计划、统计信息set autot on exp--会显示sql执行结果、执行计划set autot on stat--会显示sql执行结果、统计信息set autot trace--只显示执行计划、统计信息set autot trace exp--只显示执行计划(可能不准,sql查询并没有真正执行)set autot trace stat--只显示统计信息set autot off--关闭autotrace
2.实验验证 set autot trace exp 没有真正执行查询类sql:
SQL> set autot trace expSQL> select * from t_jingyu;Elapsed: 00:00:00.04Execution Plan----------------------------------------------------------Plan hash value: 2809386205------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1864K| 69M| 981 (2)| 00:00:12 || 1 | TABLE ACCESS FULL| T_JINGYU | 1864K| 69M| 981 (2)| 00:00:12 |------------------------------------------------------------------------------Note----- - dynamic sampling used for this statement (level=2)SQL> set autot trace SQL> select * from t_jingyu;2097152 rows selected.Elapsed: 00:00:24.89Execution Plan----------------------------------------------------------Plan hash value: 2809386205------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1864K| 69M| 981 (2)| 00:00:12 || 1 | TABLE ACCESS FULL| T_JINGYU | 1864K| 69M| 981 (2)| 00:00:12 |------------------------------------------------------------------------------Note----- - dynamic sampling used for this statement (level=2)Statistics---------------------------------------------------------- 0 recursive calls 0 db block gets 143066 consistent gets 3484 physical reads 0 redo size 51171186 bytes sent via SQL*Net to client 1538429 bytes received via SQL*Net from client 139812 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 2097152 rows processedSQL> --试验表明set autot trace exp不真正执行sql显示的执行计划,set autot trace 执行了sql显示的执行计划。
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