RAC Cluster interconnect performance
The most complex aspect of RAC tuning involves monitoring and the subsequent tuning of process associated with the Global Services Directory(GSD) . The group of processes associated with the GSD is the Global Enqueue Service(GES) and the Global Cache Service(GCS). The GSD processes communicated throught the cluster interconnects . if the cluster interconnects are not configured to process data packets efficiently, then the entire RAC implementation will perform. poorly. This is true regardless of performance-related tuning and configuration efforts in other areas.
Interconnect Traffic-sessions waiting
Sessions that wait on non-idle wait wvents that impact interconnect traffic can be monitored by a query that lists GCS waits using the global dynamic performance view gv$session_wait. You may also see these waits in a STATSPACK or AWR Repot. The major waits that are being monitored are as follows:
Global cache busy: A wait event that occurs whenever a session has to wait for an ongoing operation on the resource to complete.
Gc buffer busy : A wait event that is signaled when a process has to wait for a block to become available because another process is obtaining a resource for this block.
Buffer busy global CR: waits on a consistent read(block needed for reading) via the global cache.
To identify the sessins experiencing waits on the system, perform. the following tasks.query v$session_wait to determine whether or no any sessions are experiencing RAC-related waits (at the current time)。Identify the objects that are causing contention for these sessions. Try to modify the object or query to reduce contention.For example, query v$session_wait to determine whether or not any session are experiencing RAC cache-related waits. Note that the GV$ views are used much more to show statistics for the entire cluster, whereas the V$ views still show statistics from a single node. If you plan to use RAC, you must extend the v$ views an queries to the GV$ views for multiple nodes. Thie section is only an initial guide to help you see all of the components. This scope of this book does not cover RAC specifically,but some things that will help you tune RAC.
Select inst_id, event, p1 file, p2 block, wait_time
Where event in (‘buffer busy global CR’, ‘global cache busy’, ‘buffer busy global cache’);
The output from this query should look something like this:
Inst_id event file block wait_time
1 global cache busy 9 150 15
2 global cache busy 9 150 10
Run this query to identify objects that are causing contention for these sessions and identifying the object that corresponds to file and block for each file/block combination returned:
Select owner, segment_name, segment_type
And 150 between block_id and block_id+blocks-1
Modify the object to reduce the chances for application contention by doing the following:
Reduct the number of rows per block.
Adjust the block size to a smaller block size.
Modify initrans and freelists.
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