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有很多种方法可以用来找出哪些SQL语句需要优化，但是很久以来，最简单的方法都是分析保存在V$SQL视图中的缓存的SQL信息。通过V$SQL视图，可以确定具有高消耗时间、CUP和IO读取的SQL语句。
1.查看总消耗时间最多的前10条SQL语句
select *
from (select v.sql_id,
v.child_number,
v.sql_text,
last_load_time,
v.PARSING_USER_ID,
ROUND(v.ELAPSED_TIME / 1000000 / (CASE
WHEN (EXECUTIONS = 0 OR NVL(EXECUTIONS,1 ) = 1) THEN
1
ELSE
EXECUTIONS
END),
2) "执行时间'S'",
v.SQL_FULLTEXT,
v.cpu_time,
v.disk_reads,
rank() over(order by v.elapsed_time desc) elapsed_rank
from v$sql v ) a
where elapsed_rank <= 100 and last_load_time > to_char(sysdate - 1/24,'YYYY-MM-DD/HH:MI:SS') order by "执行时间'S'" desc
查询最近一小时内最慢的SQL:
select executions,cpu_time/1e6 as cpu_sec,elapsed_time/1e6 as elapsed_sec,round(elapsed_time/sqrt(executions)) as important,v.*
from v$sql v
where executions > 10 and last_load_time > to_char(sysdate - 1/24,'YYYY-MM-DD/HH:MI:SS')
order by important desc
2.查看CPU消耗时间最多的前10条SQL语句
select *
from (select v.sql_id,
v.elapsed_time,
rank() over(order by v.cpu_time desc) elapsed_rank
from v$sql v) a
where elapsed_rank <= 10;
3.查看消耗磁盘读取最多的前10条SQL语句
select *
from (select v.sql_id,
rank() over(order by v.disk_reads desc) elapsed_rank
from v$sql v) a
where elapsed_rank <= 10;
一、查询执行最慢的sql
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