[20210902]为什么会使用多个共享内存段.txt

[20210902]为什么会使用多个共享内存段.txt --//昨天测试kernel.sem = SEMMSL SEMMNS SEMOPM SEMMNI参数时遇到的问题,做一个记录. 1.环境: --//为了反复测试,我建立一个实例,没有数据文件. $ cat /tmp/test.ora test.__db_cache_size=1258291200 test.__oracle_base='/u01/app/oracle'#ORACLE_BASE set from environment test.__shared_pool_size=1048576000 *.db_name='test' *.processes=200 *.sga_target=2500M *.undo_management='auto' --//设置环境变量: $ export ORACLE_SID=test # egrep "^kernel.s[he]|^vm.nr_" /etc/sysctl.conf kernel.shmmax = 68719476736 kernel.shmall = 4294967296 kernel.shmmni = 4096 kernel.sem = 102 26112 204 128 vm.nr_hugepages = 404 vm.nr_overcommit_hugepages = 1300 # sysctl -p --//kernel.shmmax=68719476736, 68719476736/1024/1024/1024 = 64G,理论sga_target=2500M,11g下正常建立3个共享内存段. --//可是实际情况确实6个.通过例子说明. 2.测试: SYS@test> startup force nomount pfile='/tmp/@.ora'; ORACLE instance started. Total System Global Area 2622255104 bytes Fixed Size                  2256112 bytes Variable Size            1124074256 bytes Database Buffers         1476395008 bytes Redo Buffers               19529728 bytes $ ipcs -m ------ Shared Memory Segments -------- key        shmid      owner      perms      bytes      nattch     status 0x00000000 45645826   oracle    640        33554432   18 0x00000000 45678595   oracle    640        654311424  18 0x00000000 45711364   oracle    640        134217728  18 0x00000000 45744133   oracle    640        16777216   18 0x00000000 45776902   oracle    640        1795162112 18 0x8a931fb8 45809671   oracle    640        2097152    18 --//使用6个共享内存段. $ ipcs -m -u ------ Shared Memory Status -------- segments allocated 8 pages allocated 643681 pages resident  79750 pages swapped   0 Swap performance: 0 attempts     0 successes --//segments allocated 8 ,实际上有2个被root用户使用.如果仔细看alert日志: Starting ORACLE instance (normal) ************************ Large Pages Information ******************* Per process system memlock (soft) limit = 60 GB Total Shared Global Region in Large Pages = 802 MB (31%) Large Pages used by this instance: 401 (802 MB) Large Pages unused system wide = 3 (6144 KB) Large Pages configured system wide = 404 (808 MB) Large Page size = 2048 KB RECOMMENDATION:   Total System Global Area size is 2514 MB. For optimal performance,   prior to the next instance restart:   1. Increase the number of unused large pages by  at least 853 (page size 2048 KB, total size 1706 MB) system wide to   get 100% of the System Global Area allocated with large pages ******************************************************************** --//噢,我给hugepages仅仅404,完全不能满足需求,但是我定义了vm.nr_overcommit_hugepages = 1300,1300*2M=2600M,完全满足不需要 --//建立使用这么多的共享内存段.为什么呢? --//仔细看http://blog.itpub.net/267265/viewspace-2145481/=>0927hugepages与nr_overcommit_hugepages --//才发现要定义use_large_pages=only才可以使用. $ cat /tmp/test.ora test.__db_cache_size=1258291200 test.__oracle_base='/u01/app/oracle'#ORACLE_BASE set from environment test.__shared_pool_size=1048576000 *.db_name='test' *.processes=200 *.sga_target=2500M *.undo_management='auto' *.use_large_pages=only SYS@test> startup force nomount pfile='/tmp/@.ora'; ORACLE instance started. Total System Global Area 2622255104 bytes Fixed Size                  2256112 bytes Variable Size            1124074256 bytes Database Buffers         1476395008 bytes Redo Buffers               19529728 bytes $ ipcs -m ------ Shared Memory Segments -------- key        shmid      owner      perms      bytes      nattch     status 0x00000000 45875202   oracle    640        33554432   18 0x00000000 45907971   oracle    640        2600468480 18 0x8a931fb8 45940740   oracle    640        2097152    18 $ ipcs -m -u ------ Shared Memory Status -------- segments allocated 5 pages allocated 643681 pages resident  131681 pages swapped   0 Swap performance: 0 attempts     0 successes --//这样就对了.有时候陷入困境,思维一下子跳不出来. --//alert.log ************************ Large Pages Information ******************* Parameter use_large_pages = only Per process system memlock (soft) limit = 60 GB Total Shared Global Region in Large Pages = 2514 MB (100%) Large Pages used by this instance: 1257 (2514 MB) Large Pages unused system wide = 0 (0 KB) Large Pages configured system wide = 1257 (2514 MB) Large Page size = 2048 KB ******************************************************************** # grep -i pages /proc/meminfo AnonPages:        277180 kB AnonHugePages:     86016 kB HugePages_Total:    1257 HugePages_Free:     1000 HugePages_Rsvd:     1000 HugePages_Surp:      853 Hugepagesize:       2048 kB --//HugePages_Total: 1257,从vm.nr_overcommit_hugepages借用了853,853+404 = 1257. --//HugePages_Total-HugePages_Free+HugePages_Rsvd 就是 目前实例需要的页面数量.