数据库教程:Oracle关于TOPSQL的知识整理

–top 10 sql

  SELECT *  FROM (      SELECT b.username AS username          , a.disk_reads / DECODE(a.executions, 0, 1, a.executions) AS rds_exec_ratio          , a.sql_text AS STATEMENT      FROM v$sqlarea a, dba_users b      WHERE a.parsing_user_id = b.user_id          AND b.username = 'ZYK'      ORDER BY rds_exec_ratio DESC  )  WHERE ROWNUM < 11  ORDER BY rds_exec_ratio DESC

1. 识别’低效执行’的SQL语句

用下列SQL工具找出低效SQL:

  SELECT EXECUTIONS , DISK_READS, BUFFER_GETS,           ROUND((BUFFER_GETS-DISK_READS)/BUFFER_GETS,2) Hit_radio,           ROUND(DISK_READS/EXECUTIONS,2) Reads_per_run,           SQL_TEXT   FROM   V$SQLAREA   WHERE  EXECUTIONS>0   AND     BUFFER_GETS > 0   AND (BUFFER_GETS-DISK_READS)/BUFFER_GETS < 0.8   ORDER BY 4 DESC; 

2.查找单条语句的内存占用率

  alter system set pga_aggregate_target=10m   alter system set workarea_size_policy=auto;   select distinct * from a where rownum<500000;     select sql_text,operation_type,policy,(last_memory_used/1024/1024),   last_execution,last_tempseg_size   from v$sql i,v$sql_workarea a   where i.hash_value=a.hash_value   and sql_text='select distinct * from a where rownum<500000'; 

Top 10 by Buffer Gets:

  set linesize 100   set pagesize 100   SELECT * FROM   (SELECT substr(sql_text,1,40) sql,   buffer_gets, executions, buffer_gets/executions "Gets/Exec",   hash_value,address   FROM V$SQLAREA   WHERE buffer_gets > 10000   ORDER BY buffer_gets DESC)   WHERE rownum <= 10 ; 

Top 10 by Physical Reads:

  set linesize 100   set pagesize 100   SELECT * FROM   (SELECT substr(sql_text,1,40) sql,   disk_reads, executions, disk_reads/executions "Reads/Exec",   hash_value,address   FROM V$SQLAREA   WHERE disk_reads > 1000   ORDER BY disk_reads DESC)   WHERE rownum <= 10 ; 

Top 10 by Executions:

  set linesize 100   set pagesize 100   SELECT * FROM   (SELECT substr(sql_text,1,40) sql,   executions, rows_processed, rows_processed/executions "Rows/Exec",   hash_value,address   FROM V$SQLAREA   WHERE executions > 100   ORDER BY executions DESC)   WHERE rownum <= 10 ; 

Top 10 by Parse Calls:

  set linesize 100   set pagesize 100   SELECT * FROM   (SELECT substr(sql_text,1,40) sql,   parse_calls, executions, hash_value,address   FROM V$SQLAREA   WHERE parse_calls > 1000   ORDER BY parse_calls DESC)   WHERE rownum <= 10 ; 

Top 10 by Sharable Memory:

  set linesize 100   set pagesize 100   SELECT * FROM   (SELECT substr(sql_text,1,40) sql,   sharable_mem, executions, hash_value,address   FROM V$SQLAREA   WHERE sharable_mem > 1048576   ORDER BY sharable_mem DESC)   WHERE rownum <= 10 ; 

Top 10 by Version Count:

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  set linesize 100   set pagesize 100   SELECT * FROM   (SELECT substr(sql_text,1,40) sql,   version_count, executions, hash_value,address   FROM V$SQLAREA   WHERE version_count > 20   ORDER BY version_count DESC)   WHERE rownum <= 10 ;