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Don Burleson Blog 







RAC wait event tips

Oracle Database Tips by Donald BurlesonMay 8,  2015

Question:  What are the Oracle RAC wait events?  Which RAC wait events are the most important to monitor?

Answer:  All Oracle RAC wait events begin with "gc", indicating a global cache RAC wait event.  There are several RAC wait events that are unique to RAC.  For full scripts for monitoring Oracle RAC wait events, see the downloads in the book Oracle RAC and Grid.  The following specific RAC-related events should be monitored:

* RAC wait event - global cache open s:  A block was selected.

* RAC wait event -  global cache open x:  A block was selected for IUD.

* RAC wait event -  global cache null to s:  A block was transferred for SELECT.

* RAC wait event - global cache null to x:  A block was transferred for IUD.

* RAC wait event - global cache cr request:  A block was requested transferred for consistent read purposes.

* RAC wait event - Global Cache Service Utilization for Logical Reads.

We can also see RAC wait events in an AWR or STATSPACK report:

                                                   Total Wait    wait    Waits
Event                             Waits   Timeouts   Time (s)    (ms)     /txn
--------------------------- ----------- ---------- ---------- ------- --------
gc cr block 2-way                49,722          0         77       2      6.6
gc current block 2-way           36,791          0         52       1      4.9
gc buffer busy                    1,726          2         29      17      0.2
gc current block busy               275          0         10      37      0.0
gc cr block busy                  2,599          0          6       2      0.3
gc cr multi block request         3,096          0          3       1      0.4
gc current grant busy             7,525          0          3       0      1.0
gcs log flush sync                2,674        104          2       1      0.4
gc current grant 2-way            2,530          0          1       1      0.3

Oracle Grid and Real Application Clusters

See working examples of Oracle Grid and RAC in the book Oracle Grid and Real Application Clusters.

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