记一次oracle服务器慢问题

某天，测试突然说服务器慢。

通过xshell连接数据库服务器。连接都慢的吓人

连上后发现。

load average 和 wa不正常 io 占用了这么多cpu？

https://www.cnblogs.com/littlecharacter/p/12154587.html#anchor_top linux top说明

百度了2个sql查询下 当前耗时sql。

https://blog.csdn.net/weixin_43228740/article/details/89784981 这个里面很详细了。

果然一查 就是同事的某个sql引起的。

--查询执行最慢的50条sql
select *
 from (select sa.SQL_TEXT,
        sa.SQL_FULLTEXT,
        sa.EXECUTIONS "执行次数",
        round(sa.ELAPSED_TIME / 1000000, 2) "总执行时间",
        round(sa.ELAPSED_TIME / 1000000 / sa.EXECUTIONS, 2) "平均执行时间",
        sa.COMMAND_TYPE,
        sa.PARSING_USER_ID "用户ID",
        u.username "用户名",
        sa.HASH_VALUE
     from v$sqlarea sa
     left join all_users u
      on sa.PARSING_USER_ID = u.user_id
     where sa.EXECUTIONS > 0
     order by (sa.ELAPSED_TIME / sa.EXECUTIONS) desc)
 where rownum <= 50;

--查询最耗时的10条sql
select *
from (select v.sql_id,
v.child_number,
v.sql_text,
v.elapsed_time,
v.cpu_time,
v.disk_reads,
rank() over(order by v.cpu_time desc) elapsed_rank
from v$sql v) a
where elapsed_rank <= 10;

--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

从V$SQLAREA中查询最占用资源的查询
select b.username username,a.disk_reads reads,
a.executions exec,a.disk_reads/decode(a.executions,0,1,a.executions) rds_exec_ratio,
a.sql_text Statement
from v$sqlarea a,dba_users b
where a.parsing_user_id=b.user_id
and a.disk_reads > 100000
order by a.disk_reads desc;
用buffer_gets列来替换disk_reads列可以得到占用最多内存的sql语句的相关信息。
V$SQL是内存共享SQL区域中已经解析的SQL语句。
列出使用频率最高的5个查询
select sql_text,executions
from (select sql_text,executions,
rank() over
(order by executions desc) exec_rank
from v$sql)
where exec_rank <=5;
消耗磁盘读取最多的sql top5
select disk_reads,sql_text
from (select sql_text,disk_reads,
dense_rank() over
(order by disk_reads desc) disk_reads_rank
from v$sql)
where disk_reads_rank <=5;
找出需要大量缓冲读取（逻辑读）操作的查询
select buffer_gets,sql_text
from (select sql_text,buffer_gets,
dense_rank() over
(order by buffer_gets desc) buffer_gets_rank
from v$sql)
where buffer_gets_rank<=5;