cursor: pin S => cursor: pin S wait on X => library cache: mutex X 的优化过程
os: centos 7.4
db: oracle 11.2.0.4
版本
# cat /etc/centos-release
CentOS Linux release 7.4.1708 (Core)
#
# su - oracle
Last login: Tue Jan 21 03:40:05 CST 2020 on pts/0
$ sqlplus / as sysdba;
SQL*Plus: Release 11.2.0.4.0 Production on Mon Feb 3 10:29:09 2020
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options
SQL> set lines 300;
SQL> set pages 300;
SQL>
SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
PL/SQL Release 11.2.0.4.0 - Production
CORE 11.2.0.4.0 Production
TNS for Linux: Version 11.2.0.4.0 - Production
NLSRTL Version 11.2.0.4.0 - Production
SQL>
准备基础表、数据
$ sqlplus scott2/oracle
SQL*Plus: Release 11.2.0.4.0 Production on Tue Mar 3 02:05:48 2020
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options
SQL>
SQL> set lines 300;
set pages 300;
SQL> create table tmp_t0 (
c0 integer not null,
c1 varchar2(100) not null,
c2 varchar2(2000)
);
SQL> alter table TMP_T0 add constraint pk_tmp_t0 primary key (C0);
SQL> insert into tmp_t0
select level as id,
level||'_'||level as name,
level||'_'||level||'_'||level as memo
from dual
connect by level <=1000000
;
SQL> commit;
准备压测脚本
# su - oracle
$ vi select.sh
#!/bin/bash
for((i=1;i<=100;i++));
do
(
sqlplus -S /nolog <cursor: pin S
开始执行并发脚本
$ ./select.sh
SQL> select s."EVENT#",
s."EVENT",
count(1)
from v$session s
where 1=1
and s."USERNAME"='SCOTT2'
group by s."EVENT#",
s."EVENT"
;
EVENT# EVENT COUNT(1)
---------- ---------------------------------------------------------------- ----------
354 SQL*Net message from client 6
281 cursor: pin S 100
350 SQL*Net message to client 1
优化 cursor: pin S
$ vi select_1.sh
#!/bin/bash
for((i=1;i<=100;i++));
do
(
sqlplus -S /nolog <开始压测
$ chmod 755 ./select_1.sh
$ ./select_1.sh
SQL> select s."EVENT#",
s."EVENT",
count(1)
from v$session s
where 1=1
and s."USERNAME"='SCOTT2'
group by s."EVENT#",
s."EVENT"
;
EVENT# EVENT COUNT(1)
---------- ---------------------------------------------------------------- ----------
289 library cache: mutex X 3
1021 kksfbc child completion 11
354 SQL*Net message from client 6
282 cursor: pin S wait on X 83
350 SQL*Net message to client 1
288 library cache load lock 1
287 library cache lock 2
7 rows selected.
出现了其它的等待事件
SQL> select s."EVENT#",
s."EVENT",
s.sql_id,
sa."SQL_TEXT"
from v$session s
left outer join v$sqlarea sa
on s.sql_id = sa.sql_id
where 1=1
and s."USERNAME"='SCOTT2'
;
EVENT# EVENT SQL_ID SQL_TEXT
---------- ---------------------------------------------------------------- -------------------------------------------------------------------------------------
282 cursor: pin S wait on X 6a4x85vsp51k6 select/*+ 182941*/ c1 from tmp_t0 t0 where 1=1 and t0.c0=:1
282 cursor: pin S wait on X 0ut10d7fu26wx select/*+ 182945*/ c1 from tmp_t0 t0 where 1=1 and t0.c0=:1
282 cursor: pin S wait on X 82mmhxj4nygxn select/*+ 182940*/ c1 from tmp_t0 t0 where 1=1 and t0.c0=:1
1021 kksfbc child completion 38ac1y5k200ba select/*+ 182939*/ c1 from tmp_t0 t0 where 1=1 and t0.c0=:1
282 cursor: pin S wait on X 38ac1y5k200ba select/*+ 182939*/ c1 from tmp_t0 t0 where 1=1 and t0.c0=:1
282 cursor: pin S wait on X 331tu1famzw32 select/*+ 182944*/ c1 from tmp_t0 t0 where 1=1 and t0.c0=:1
282 cursor: pin S wait on X 331tu1famzw32 select/*+ 182944*/ c1 from tmp_t0 t0 where 1=1 and t0.c0=:1
287 library cache lock 0ut10d7fu26wx select/*+ 182945*/ c1 from tmp_t0 t0 where 1=1 and t0.c0=:1
282 cursor: pin S wait on X 02c2vx389dyc2 select/*+ 182953*/ c1 from tmp_t0 t0 where 1=1 and t0.c0=:1
107 rows selected.
进一步优化 cursor: pin S wait on X
cursor: pin S wait on X 是硬解析过多，进一步优化下
$ vi select_2.sh
#!/bin/bash
for((i=1;i<=100;i++));
do
(
sqlplus -S /nolog <开始压测
$ chmod 755 ./select_2.sh
$ ./select_2.sh
SQL> select s."EVENT#",
s."EVENT",
count(1)
from v$session s
where 1=1
and s."USERNAME"='SCOTT2'
group by s."EVENT#",
s."EVENT"
;
EVENT# EVENT COUNT(1)
---------- ---------------------------------------------------------------- ----------
289 library cache: mutex X 93
354 SQL*Net message from client 6
279 cursor: mutex S 3
281 cursor: pin S 4
350 SQL*Net message to client 1
又出现事件 library cache: mutex X
SQL> select s."EVENT#",
s."EVENT",
s.sql_id,
sa."SQL_TEXT"
from v$session s
left outer join v$sqlarea sa
on s.sql_id = sa.sql_id
where 1=1
and s."USERNAME"='SCOTT2'
;
继续优化 library cache: mutex X
Library cache: mutex等待事件产生常见原因：
1 os资源不足(cpu、内存)
2 sga设置不合理，shared_pool不足，或动态调整导致hard parse
3 hot object contention
4 hard parse
5 sql high version count 由于子游标太多，扫描时会形成锁
6 library cache object失效导致重编译
7 bug
参考：