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Tuesday, March 2, 2010

DRM - Dynamic Resource Mastering

DRM - Dynamic Resource Mastering

When using Real application Clusters (RAC), Each instance has its own SGA and buffer cache. RAC will ensure that these block changes are co-ordinated to maximize performance and to ensure data intergrity. Each copy of the buffer also called as a cache resource has a master which is one of the nodes of the cluster.

In database releases before 10g (10.1.0.2) once a cache resource is mastered on an instance, a re-mastering or a change in the master would take place only during a reconfiguration that would happen automatically during both normal operations like instance startup or instance shutdown or abnormal events like Node eviction by Cluster Manager. So if Node B is the master of a cache resource, this resource will remain mastered on Node B until reconfiguration.

10g introduces a concept of resource remastering via DRM. With DRM a resource can be re-mastered on another node say from Node B to Node A if it is found that the cache resource is accessed more frequently from Node A. A reconfiguration is no longer the only reason for a resource to be re-mastered.

In 10gR1 DRM is driven by affinity of files and in 10gR2 it is based on objects.

Associated Bug with DRM on 10g:
Instance will terminate with the below error in alert log:

ORA-00481: LMON process terminated with error
also

Instance fails during DRM with lmon reporting kjfcdrmrfg: SYNC TIMEOUT (522650, 521749, 900), step 34
and alert log showing:
Fri Feb XX 06:02:22 2010
Errors in file /bdump/sid1_lmon_1085658.trc:
ORA-00481: LMON process terminated with error

AWR reports shows:

Event Waits %Time -outs Total Wait Time (s) Avg wait (ms) Waits /txn
gc remaster 471 97.88 898 1908 0.22


FIX :--

There is not currently a patch for bug 6960699 on AIX.
The workaround is to disable DRM by setting on all instances:
_gc_affinity_time=0
_gc_undo_affinity=FALSE

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