High "gc cr grant 2-way" / "gc current block 2-way" Wait due to Different CPU Count on Cluster Nodes (Doc ID 1911398.1)

Last updated on DECEMBER 10, 2023

Applies to:

Symptoms

In this case, it is 2-node RAC (problem could happen for multiple nodes) with high gc wait events reported and performance is slow intermittently for both instances:

awrrpt_1_38136_38138.html:

                Snap Id        Snap Time    Sessions Cursors/Session
Begin Snap:     38136  26-Jun-14 08:00:32      2765      2.3
End Snap:       38138  26-Jun-14 09:00:34      2795      2.3
Elapsed:              60.03 (mins) 
DB Time:           2,295.65 (mins) 

Top 5 Timed Foreground Events

Event                             Waits     Time(s)  Avg wait (ms) % DB time Wait Class
gc cr grant 2-way               361,302     26,758         74         19.43   Cluster
gc current block 2-way          685,849     19,607         29         14.23   Cluster
gc buffer busy acquire           46,534     16,829        362         12.22   Cluster
db file sequential read       3,029,992     16,728          6         12.14   User I/O
DB CPU                                      15,400                    11.18

ASH report shows the intermittent nature of the gc wait:

                        Slot  Event
Slot Time (Duration)    Count Event                             Count % Event
-------------------- -------- ------------------------------ -------- -------
08:00:00   (5.0 min)    1,276 gc cr grant 2-way                   381    2.67
                              gc current block 2-way              200    1.40
                              gc buffer busy acquire              147    1.03
08:05:00   (5.0 min)    3,065 gc cr grant 2-way                   955    6.70
                              gc current block 2-way              578    4.06
                              gc buffer busy acquire              528    3.70
08:10:00   (5.0 min)      396 CPU + Wait for CPU                  188    1.32
                              db file sequential read             106    0.74
                              gc current block 2-way               18    0.13
08:15:00   (5.0 min)      505 CPU + Wait for CPU                  251    1.76
                              db file sequential read             117    0.82
                              enq: TX - row lock contention        42    0.29
08:20:00   (5.0 min)      632 CPU + Wait for CPU                  299    2.10
                              db file sequential read             142    1.00
                              gc cr grant 2-way                    39    0.27
08:25:00   (5.0 min)      478 CPU + Wait for CPU                  237    1.66
                              db file sequential read             137    0.96
                              enq: TX - row lock contention        32    0.22
08:30:00   (5.0 min)    4,316 gc cr grant 2-way                 1,161    8.15
                              gc buffer busy acquire              945    6.63
                              gc current block 2-way              644    4.52
08:35:00   (5.0 min)    1,915 gc current block 2-way              368    2.58
                              gc cr grant 2-way                   318    2.23
                              CPU + Wait for CPU                  204    1.43
08:40:00   (5.0 min)      370 CPU + Wait for CPU                  146    1.02
                              db file sequential read             127    0.89
                              gc current block 2-way               26    0.18

There is no workload change or major application change during this time period.

_max_cr_rollbacks is already set to 200 per <Note 1630755.1>: AWR shows high "gc cr grant 2-way" wait and the trace file shows that lms has not moved for more than 60 seconds

Cause

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