Database Reference
In-Depth Information
Elapsed times include waiting on the following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- -------------
gc cr grant 2-way 271931 1.39 905.49
...
gc cr grant congested 4249 1.47 150.58
...
gc current grant 2-way 98 0.00 0.22
Overview of DRM Processing
RAC background processes keep track of global cache lock requests at an object level. I should emphasize that it is
not object access but rather gc lock requests on an object that are tracked. If the number of BL lock requests from an
instance exceeds a threshold in an observation window, then DRM is triggered for that object. After the completion
of DRM, the object will be locally mastered and future access to that object from that instance will use affinity-locking
scheme, reducing waits for grants. Three RAC background processes are at the heart of DRM implementation:
1.
LCK0 process maintains object-level statistics and decides if remastering should be
triggered on an object.
2.
If an object is chosen, a request is queued. LMD process reads the request queue and
initiates GRD freeze. In the following LMD trace file, pkey indicates the object_id of the
remastered object. Dissolve pkey means that all resources currently mastered by the local
instance must be removed from local instance memory.
*** 2010-01-08 19:41:26.726
* kjdrchkdrm: found an RM request in the request queue
Dissolve pkey 6984390
*** 2010-01-08 19:41:26.727
Begin DRM(189) - dissolve pkey 6984390 from 2 oscan 1.1
ftd received from node 1 (8/0.30.0)
ftd received from node 0 (8/0.30.0)
ftd received from node 3 (8/0.30.0)
all ftds received
3.
LMON coordinates reconfiguration using LMS processes. Reconfiguration goes through
many stages. DRM reconfiguration is similar to the reconfiguration triggered after
the instance crash, but less severe. Reconfiguration triggered after an instance crash
will remaster every resource mastered by the failed instance, whereas reconfiguration
triggered for DRM will remaster only the resource identified by LCK0 process.
*** 2010-01-08 19:41:26.793
Begin DRM(189)
sent syncr inc 8 lvl 5577 to 0 (8,0/31/0)
synca inc 8 lvl 5577 rcvd (8.0)
View x$object_policy_statistics externalizes the BL lock requests and shows locking activity at the object level.
As visible in the query output from x$object_policy_statistics, there were many Shared BL lock requests on object
12189604. In the following output, columns SOPENS and XOPENS track counts of BL lock requests in shared and
exclusive mode, respectively.
