Oracle10g New Feature:CRS(Cluster Ready Services)

Oracle10g CRS(Cluster Ready Services)是Oracle10g RAC的一个新特性，用以提供标准的群集服务接口。

在以前的版本中，Oracle RAC必须借助第三方Cluster软件，但是从Oracle10g开始，我们有了新的选择。

CRS就是这样一个替代产品，用以提供RAC环境中的群集服务。



CRS是一个单独的产品，在构建RAC环境中，需要单独安装。



系统启动以后，CRS会自动启动，启动主要由/etc/init.d中的几个脚本完成:

[eygle@raclinux1 init.d]$ ll init*
-r-xr-xr-x  1 root root  1951 Jun 27 13:27 init.crs
-r-xr-xr-x  1 root root  4735 Jun 27 20:32 init.crsd
-r-xr-xr-x  1 root root 35401 Jun 27 13:27 init.cssd
-r-xr-xr-x  1 root root  3197 Jun 27 13:27 init.evmd

CRS启动的三个主要的后台进程为:

[oracle@raclinux1 bin]$ ps -ef|grep d.bin
root      3140     1  0 23:13         00:00:00 /u01/app/oracle/product/10.2.0/crs/bin/crsd.bin
oracle    3884  3062  0 23:14         00:00:00 /u01/app/oracle/product/10.2.0/crs/bin/evmd.bin
oracle    4017  3983  0 23:14         00:00:00 /u01/app/oracle/product/10.2.0/crs/bin/ocssd.bin
oracle   21117 13799  0 23:29 pts/1   00:00:00 grep d.bin

这几个进程的主要作用如下:

CRSD:
- Engine for HA operation 
- Manages 'application resources'
- Starts, stops, and fails 'application resources' over
- Spawns separate 'actions' to start/stop/check application resources
- Maintains configuration profiles in the OCR (Oracle Configuration Repository)
- Stores current known state in the OCR.
- Runs as root
- Is restarted automatically on failure
OCSSD:
- OCSSD is part of RAC and Single Instance with ASM
- Provides access to node membership
- Provides group services
- Provides basic cluster locking
- Integrates with existing vendor clusteware, when present
- Can also runs without integration to vendor clustware
- Runs as Oracle.
- Failure exit causes machine reboot.  
--- This is a feature to prevent data corruption in event of a split brain.

注意，ocssd进程在单实例ASM系统中也可以见到，以下是我的一个单实例ASM系统，ocssd进程同样存在:

bash-2.03# ps -ef|grep _+ASM
  oracle  3264     1  0   Aug 25 ?        0:01 asm_lgwr_+ASM
    root 12669  8167  0 11:58:56 pts/1    0:00 grep _+ASM
  oracle  3270     1  0   Aug 25 ?        0:00 asm_rbal_+ASM
  oracle  3266     1  0   Aug 25 ?        0:05 asm_ckpt_+ASM
  oracle  3268     1  0   Aug 25 ?        0:00 asm_smon_+ASM
  oracle  3262     1  0   Aug 25 ?        0:00 asm_dbw0_+ASM
  oracle  3258     1  0   Aug 25 ?        0:00 asm_pmon_+ASM
  oracle  3260     1  0   Aug 25 ?        0:00 asm_mman_+ASM
bash-2.03# ps -ef|grep ocssd
    root 12672  8167  0 11:59:01 pts/1    0:00 grep ocssd
  oracle  5374     1  0   Apr 07 ?        0:01 /opt/oracle/product/10.1.0/bin/ocssd.bin
bash-2.03# 

ocssd进程非常重要，如果该进程异常中止，会导致系统crash。

在某些极端情况下，如果ocssd无法正常启动，会导致操作系统循环重启。这时候需要DBA介入进行一些特殊处理。

EVMD:
- Generates events when things happen
- Spawns a permanent child evmlogger
- Evmlogger, on demand, spawns children
- Scans callout directory and invokes callouts.
- Runs as Oracle.
- Restarted automatically on failure