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Oracle 后台进程MMAN、MMON、MMNL

DB数据库 admin 2018年9月1日 13:05 565 0 个评论

在Oracle10g中,有两个后台进程是新增的,这里我想说的是MMON和MMNL。
在Oracle不同的文档中,对这两个进程的解释存在歧义。
MMON 应该是 Memory Monitor 的缩写,但是在有的文档中被记录为Manageability Monitor ,这应当是10g早期版本中的称呼,只不过后来发生了变更。
这个进程的主要作用如下:
The memory monitor (MMON) process was introduced in 10g and is associated with the Automatic Workload Repository new features used for automatic problem detection and self-tuning. MMON writes out the required statistics for AWR on a scheduled basis.

另外一个进程是 MMNL ,是 Memory Monitor Light (MMNL) 的缩写,在部分文档中记录为 Manageability Monitor Light .
这个进程的作用如下:
The Memory Monitor Light (MMNL) process is a new process in 10g which works with the Automatic Workload Repository new features (AWR) to write out full statistics buffers to disk as needed.

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。
在文档上,Oracle说,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.

这里的内部任务显然包括自动的内存调整,但是不排除还有其他使命。
当进行内存调整时,有一个等待事件于此有关:
SGA: MMAN sleep for component shrink

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:
*** 2009-12-22 15:00:04.484
WAIT #0: nam='rdbms ipc message' ela= 2999944 timeout=300 p2=0 p3=0 obj#=-1 tim=9809590317
WAIT #0: nam='rdbms ipc message' ela= 2999773 timeout=300 p2=0 p3=0 obj#=-1 tim=9812737808
WAIT #0: nam='rdbms ipc message' ela= 2999664 timeout=300 p2=0 p3=0 obj#=-1 tim=9815814982
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10045 component id=6 current size=8 target size=7 obj#=-1 tim=9815936073
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10581 component id=6 current size=8 target size=7 obj#=-1 tim=9815946809
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10541 component id=6 current size=8 target size=7 obj#=-1 tim=9815957544
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10655 component id=6 current size=8 target size=7 obj#=-1 tim=9815968290
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10649 component id=6 current size=8 target size=7 obj#=-1 tim=9815979031
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10645 component id=6 current size=8 target size=7 obj#=-1 tim=9815989770
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10678 component id=6 current size=8 target size=7 obj#=-1 tim=9816000516
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10661 component id=6 current size=8 target size=7 obj#=-1 tim=9816011260
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10644 component id=6 current size=8 target size=7 obj#=-1 tim=9816022006
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10623 component id=6 current size=8 target size=7 obj#=-1 tim=9816032746
WAIT #0: nam='SGA: MMAN sleep for component shrink' ela= 10664 component id=6 current size=8 target size=7 obj#=-1 tim=9816043506
WAIT #0: nam='rdbms ipc message' ela= 2449387 timeout=245 p2=0 p3=0 obj#=-1 tim=9818925363
然而在很多繁忙的环境中,自动的内存调整会成为一个负担,所以很多用户禁用了这一功能。



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