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:

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 ;