Oracle数据库大量library cache: mutex X及latch: shared pool问题排查一例
业务系统数据库夯住，数据库内大量的library cache: mutex X及latch: shared pool等待，alert日志信息如下
Tue Sep ::
WARNING: inbound connection timed out (ORA-)
Tue Sep ::
WARNING: inbound connection timed out (ORA-)
Tue Sep ::
WARNING: inbound connection timed out (ORA-)
Tue Sep ::
WARNING: inbound connection timed out (ORA-)
数据库历史session统计如下
latch: shared pool
library cache: mutex X
library cache: mutex X
6hurnha5k9qb6 latch: shared pool
latch: shared pool
0rs4yunhszr7w latch: shared pool
b7fy2a0snpja9 library cache: mutex X
null event
latch: shared pool
0rs4yunhszr7w latch: shared pool
library cache: mutex X
6hurnha5k9qb6 latch: shared pool
b7fy2a0snpja9 library cache: mutex X
latch: shared pool
library cache: mutex X
null event
latch: shared pool
latch: shared pool
0rs4yunhszr7w latch: shared pool
b7fy2a0snpja9 library cache: mutex X
6hurnha5k9qb6 latch: shared pool
library cache: mutex X
library cache: mutex X
阻塞会话明细
SQL> select event,sql_id,USER_ID,program from gV$active_session_history a where INST_ID= and SESSION_ID= and to_char(a.sample_time, 'yyyymmddHH24mi')=;
latch: shared pool 6hurnha5k9qb6 oracle@ZJHZ-px-xxx- (J002)
latch: shared pool 6hurnha5k9qb6 oracle@ZJHZ-px-xxx- (J002)
latch: shared pool 6hurnha5k9qb6 oracle@ZJHZ-px-xxx- (J002)
latch: shared pool 6hurnha5k9qb6 oracle@ZJHZ-px-xxx- (J002)
latch: shared pool 6hurnha5k9qb6 oracle@ZJHZ-px-xxx- (J002)
latch: shared pool 6hurnha5k9qb6 oracle@ZJHZ-px-xxx- (J002)
latch: shared pool 6hurnha5k9qb6 oracle@ZJHZ-px-xxx- (J002)
latch: shared pool 6hurnha5k9qb6 oracle@ZJHZ-px-xxx- (J002)
latch: shared pool 6hurnha5k9qb6 oracle@ZJHZ-px-xxx- (J002) SQL> select event,sql_id,USER_ID,program from gV$active_session_history a where INST_ID= and SESSION_ID=352and to_char(a.sample_time, 'yyyymmddHH24mi')=;
EVENT SQL_ID USER_ID PROGRAM
------------------------------ ------------- ---------- ------------------------------------------------
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
oracle@ZJHZ-px-xxx- (MMAN)
MMAN进程是Oracle 10g引入用于进行内存管理的进程，在进行动态内存调整时，这个进程要发挥其作用,这个进程的作用是内部数据库任务的执行者：MMAN is used for internal database tasks.
MMAN to wait and post itself for satisfying an auto-tuned memory request while trying to fully free a component's quiesced granules. In Release 10.1, the name of this event was 'wait for SGA component shrink'.
在后台转储跟踪，可以看到MMAN进程的等待：
WAIT #: nam='SGA: MMAN sleep for component shrink' ela= component id= current size= target size= obj#=- tim=
WAIT #: nam='SGA: MMAN sleep for component shrink' ela= component id= current size= target size= obj#=- tim=
WAIT #: nam='SGA: MMAN sleep for component shrink' ela= component id= current size= target size= obj#=- tim=
WAIT #: nam='SGA: MMAN sleep for component shrink' ela= component id= current size= target size= obj#=- tim=
WAIT #: nam='SGA: MMAN sleep for component shrink' ela= component id= current size= target size= obj#=- tim=
查询数据库最近内存调整记录
SQL> select COMPONENT,
2 STATUS,
3 OPER_TYPE,
4 OPER_MODE,
5 PARAMETER,
6 round(INITIAL_SIZE/1024/1024,2) INITIAL_mb ,
7 round(TARGET_SIZE/1024/1024,2) TARGET_MB,
8 round(FINAL_SIZE/1024/1024,2) FINAL_mb,
9 to_char(START_TIME, 'yyyy-mm-dd hh24:mi:ss') START_TIME,
10 to_char(END_TIME, 'yyyy-mm-dd hh24:mi:ss') END_TIME
11 from V$MEMORY_RESIZE_OPS
12 where START_TIME > to_date('','yyyymmddhh24')
13 order by END_TIME;
COMPONENT STATUS OPER_TYPE OPER_MODE PARAMETER INITIAL_MB TARGET_MB FINAL_MB START_TIME END_TIME
------------------------------ --------- ------------- --------- ------------------------------ ---------- ---------- ---------- ------------------- -------------------
shared pool COMPLETE SHRINK DEFERRED shared_pool_size 2752 2624 2624 2017-09-26 22:01:21 2017-09-26 22:10:07
DEFAULT buffer cache COMPLETE GROW DEFERRED db_cache_size 1536 1664 1664 2017-09-26 22:01:21 2017-09-26 22:10:07
DEFAULT buffer cache COMPLETE SHRINK DEFERRED db_cache_size 1664 1536 1536 2017-09-26 22:23:11 2017-09-26 22:23:13
shared pool COMPLETE GROW DEFERRED shared_pool_size 2624 2752 2752 2017-09-26 22:23:11 2017-09-26 22:23:13
至此问题定位，是由于SGA内存自动调整导致数据库异常
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