Oracle Clusterware Diagnosis - Expert Oracle RAC Performance Diagnostics and Tuning - page 536

OCR also maintains application resources defined within the Oracle Clusterware; specifically, database, instances,
services, and node applications 2 information. Oracle Clusterware reads the ocr.loc file ( ocr.loc file is located in the
/etc/oracle/ directory on Linux and Unix systems; on Windows systems the pointer is located in the registry) for the
location of the OCR file and to determine what applications resources need to be started as well as the nodes on which
to start them.
[root@ssky3l11p1 ~]# cat /etc/oracle/ocr.loc
ocrconfig_loc=+GRID_DATA
local_only=FALSE
Here is an extract from the OCR file.
[SYSTEM.crs.user_default_dir]
ORATEXT : /u01/app/12.1.0/grid/crs/public
SECURITY : {USER_PERMISSION : PROCR_ALL_ACCESS, GROUP_PERMISSION : PROCR_READ,
OTHER_PERMISSION : PROCR_READ, USER_NAME : root, GROUP_NAME : root}
[SYSTEM.ORA_CRS_HOME]
ORATEXT : /u01/app/12.1.0/grid
SECURITY : {USER_PERMISSION : PROCR_ALL_ACCESS, GROUP_PERMISSION : PROCR_READ,
OTHER_PERMISSION : PROCR_READ, USER_NAME : root, GROUP_NAME : root}
Oracle uses distributed shared-cache architecture during cluster management to optimize queries against the
cluster registry. Each node maintains a copy of the OCR in memory. Oracle Clusterware uses a background process to
access the OCR cache. Only one OCR process (designated as the master) in the cluster performs any disk read/write
activity. Once the master OCR process reads any new information, it performs a refresh of the local OCR cache and
the OCR cache on other nodes in the cluster. Since the OCR cache is distributed across all nodes in the cluster, OCR
clients communicate directly with the local OCR process on the node to obtain required information. While reading
from the registry is coordinated through the master process across the cluster, any write (update) to disk or registry
activity is not centralized—it is performed by the local OCR process, where the client is attached.
The Oracle Local Registry (OLR)
In Oracle Database 11g Release 2, Oracle introduced a different kind of registry called the OLR. OLR files
contain information pertaining to all tiers of the clustered database for a specific node. OLR resides on every
node (Figure 16-1 ) in the cluster and manages clusterware configuration information for each particular node.
A dissection of the OLR file would reveal various parameters stored as name-value pairs, which are used and
maintained at different levels of the architecture.
While the OLR contains a subset of the information contained in the OCR, the OLR file is maintained on the local
storage under the GRID_HOME . Oracle Clusterware reads the olr.loc file ( olr.loc file is located in the /etc/oracle/
directory on Linux and Unix systems; on Windows systems the pointer is located in the registry) for the location of the
local registry.
[root@ssky3l11p1 ~]# cat /etc/oracle/olr.loc
olrconfig_loc=/u01/app/12.1.0/grid/cdata/ssky3l11p1.olr
crs_home=/u01/app/12.1.0/grid
[root@ssky3l11p1 ~]# ls -ltr $GRID_HOME/cdata/ssky3l11p1.olr
-rw------- 1 root oinstall 503484416 Jan 14 20:31 /u01/app/12.1.0/grid/cdata/ssky3l11p1.olr
2 The various processes such as the VIP, ONS, GSD, and listener are called node applications .