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Don Burleson Blog 







Oracle High Availability Services (OHAS)

Oracle Database Tips by Donald BurlesonDecember 22, 2015

Staring in Oracle 11g Real Application Clusters (RAC), we see a new process called Oracle High Availability Services or OHAS for short.

OHAS is implemented via a new daemon process which is called ohasd on the OS layer, and the 11g documentation notes that this Oracle High Availability Services Daemon (OHASD) anchors the lower part of the Oracle Clusterware stack, which consists of processes that facilitate cluster operations in RAC databases.  This includes the GPNPD, GIPC, MDNS and GNS background processes.

It appears that RAC DBA's will continue to use the traditional crsctl commands for cluster management and that there are no direct commands for Oracle High Availability Services.

The 11g docs note the jobs of the OHAS Oracle High Availability Services Stack:

The list in this section describes the processes that comprise the Oracle High Availability Services stack.

  • Grid Plug and Play (GPNPD): GPNPD provides access to the Grid Plug and Play profile, and coordinates updates to the profile among the nodes of the cluster to ensure that all of the nodes node have the most recent profile.

  • Grid Interprocess Communication (GIPC): A helper daemon for the communications infrastructure. Currently has no functionality; to be activated in a later release.

  • Multicast Domain Name Service (mDNS): Allows DNS requests. The mDNS process is a background process on Linux and UNIX, and a service on Windows.

  • Oracle Grid Naming Service (GNS): A gateway between the cluster mDNS and external DNS servers. The gnsd process performs name resolution within the cluster.

Enabling Oracle High Availability Services (OHAS) in 11gr2 and beyond

To enable OHAS for each RAC node, you issue the crsctl enable crs command, and this will cause OHAS to autostart when each node re-boots.  To verify that OHAS is running, check for the CRS-4123 message in your alert log:

CRS-4123: Oracle High Availability Services has been started.
ohasd is starting


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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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