MMAN blocker
Date: Thu, 25 Jul 2019 10:33:47 +0000
Message-ID: <15691_1564050844_5D39859C_15691_1838_1_fbc2f905d6414512a58fca5b0f59a7d5_at_vontobel.com>
We got the first ORA-04031 at 10 PM for a tiny memory allocation of 40 bytes:
2019-07-22T22:00:48.776288+02:00
Errors in file /u00/oracle/orabase/diag/rdbms/DB1_site1/DB1/trace/DB1_ora_28267.trc (incident=230935):
ORA-04031: unable to allocate 40 bytes of shared memory ("shared pool","GV$SQL","KGLH0^6b31dba1","kglHeapInitialize:temp")
The problem persisted until we restarted the instance around half an hour later, even though we, at least at some point, had enough free memory in both subpools:
2019-07-22T22:35:41.573895+02:00
Errors in file /u00/oracle/orabase/diag/rdbms/DB1_site1/DB1/trace/DB1_cjq0_29161.trc:
ORA-04031: unable to allocate bytes of shared memory ("","","","")
ORA-04031: unable to allocate 40 bytes of shared memory ("shared pool","unknown object","KGLH0^c10d8511","kglHeapInitialize:temp")
TOP 10 MEMORY USES FOR SGA HEAP SUB POOL 1
"object queue hash buckets " 192 MB 28%
"free memory " 176 MB 26%
"dbwriter coalesce buffer " 48 MB 7%
"kglsim object batch " 41 MB 6%
"ASH buffers " 32 MB 5%
"kglsim heap " 22 MB 3%
"execution ID memory " 19 MB 3%
"dirty object counts array " 12 MB 2%
"KGLH0 " 7714 KB 1%
"event statistics per sess " 7485 KB 1%
free memory 176 MB memory alloc. 512 MB Sub total 688 MB ============================================== ==============================================TOP 10 MEMORY USES FOR SGA HEAP SUB POOL 2
"free memory " 230 MB 35%
"Checkpoint queue " 96 MB 15%
"keomg: entry list " 59 MB 9%
"kglsim object batch " 41 MB 6%
"ASH buffers " 30 MB 5%
"kglsim heap " 22 MB 3%
"execution ID memory " 19 MB 3%
"event statistics per sess " 7485 KB 1%
"simulator latch/bucket st " 7424 KB 1%
"write state object " 7420 KB 1%
free memory 230 MB memory alloc. 426 MB Sub total 656 MB ==============================================
Many sessions were affected. Also, creating new sessions wasn't possible.
According to the system dump the affected sessions were waiting on MMAN to finish a memory resizing operation:
...
7: MMAN ospid 26758 sid 71 ser 33258, waiting for 'rdbms ipc message'
...
But MMAN seemed idle ('rdbms ipc message').
I concluded following:
My questions are:
72: CJQ0 ospid 29161 sid 721 ser 22160, waiting for 'SGA: allocation forcing component growth'
Blocked by inst: 1, sid: 71, ser: 33258
Final Blocker inst: 1, sid: 71, ser: 33258
...
1. Due to the shared pool shortage MMAN started growing it.
2. At some point, there was enough memory to fulfill the requests, but they were failing, because the sessions were waiting on MMAN to finish the resizing.
1. Are my conclusions correct?
2. How does a session makes a decision whether to allocate a chunk from the free memory or to wait on 'SGA: allocation forcing component growth'?
Best regards,
Nenad
https://nenadnoveljic.com/blog/
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