Re: Patch to address creation of PgStat* contexts with null parent context - Mailing list pgsql-hackers
From | Zhang Mingli |
---|---|
Subject | Re: Patch to address creation of PgStat* contexts with null parent context |
Date | |
Msg-id | fd7cc8ae-89d4-44b9-ba1d-7371268d011f@Spark Whole thread Raw |
In response to | Patch to address creation of PgStat* contexts with null parent context (Reid Thompson <reid.thompson@crunchydata.com>) |
Responses |
Re: Patch to address creation of PgStat* contexts with null parent context
|
List | pgsql-hackers |
Hi,
On Jul 28, 2022, 21:30 +0800, Reid Thompson <reid.thompson@crunchydata.com>, wrote:
On Jul 28, 2022, 21:30 +0800, Reid Thompson <reid.thompson@crunchydata.com>, wrote:
Hi,
There are instances where pgstat_setup_memcxt() and
pgstat_prep_pending_entry() are invoked before the CacheMemoryContext
has been created. This results in PgStat* contexts being created
without a parent context. Most easily reproduced/seen in autovacuum
worker via pgstat_setup_memcxt().
Attached is a patch to address this.
To see the issue one can add a line similar to this to the top of
MemoryContextCreate() in mcxt.c
fprintf(stderr, "pid: %d ctxname: %s parent is %s CacheMemoryContext is %s\n", MyProcPid, name, parent == NULL ? "NULL" : "not NULL", CacheMemoryContext == NULL ? "NULL" : "Not NULL")
and startup postgres and grep for the above after autovacuum workers
have been invoked
...snip...
pid: 1427756 ctxname: PgStat Pending parent is NULL CacheMemoryContext is NULL
pid: 1427756 ctxname: PgStat Shared Ref parent is NULL CacheMemoryContext is NULL
...snip...
or
startup postgres, attach gdb to postgres following child, break at
pgstat_setup_memcxt and wait for autovacuum worker to start...
...snip...
─── Source ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
384 AllocSetContextCreateInternal(MemoryContext parent,
385 const char *name,
386 Size minContextSize,
387 Size initBlockSize,
388 Size maxBlockSize)
389 {
390 int freeListIndex;
391 Size firstBlockSize;
392 AllocSet set;
393 AllocBlock block;
─── Stack ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
[0] from 0x000055b7e4088b40 in AllocSetContextCreateInternal+0 at /home/rthompso/src/git/postgres/src/backend/utils/mmgr/aset.c:389
[1] from 0x000055b7e3f41c88 in pgstat_setup_memcxt+2544 at /home/rthompso/src/git/postgres/src/backend/utils/activity/pgstat_shmem.c:979
[2] from 0x000055b7e3f41c88 in pgstat_get_entry_ref+2648 at /home/rthompso/src/git/postgres/src/backend/utils/activity/pgstat_shmem.c:410
[3] from 0x000055b7e3f420ea in pgstat_get_entry_ref_locked+26 at /home/rthompso/src/git/postgres/src/backend/utils/activity/pgstat_shmem.c:598
[4] from 0x000055b7e3f3e2c4 in pgstat_report_autovac+36 at /home/rthompso/src/git/postgres/src/backend/utils/activity/pgstat_database.c:68
[5] from 0x000055b7e3e7f267 in AutoVacWorkerMain+807 at /home/rthompso/src/git/postgres/src/backend/postmaster/autovacuum.c:1694
[6] from 0x000055b7e3e7f435 in StartAutoVacWorker+133 at /home/rthompso/src/git/postgres/src/backend/postmaster/autovacuum.c:1493
[7] from 0x000055b7e3e87367 in StartAutovacuumWorker+557 at /home/rthompso/src/git/postgres/src/backend/postmaster/postmaster.c:5539
[8] from 0x000055b7e3e87367 in sigusr1_handler+935 at /home/rthompso/src/git/postgres/src/backend/postmaster/postmaster.c:5244
[9] from 0x00007fb02bca7420 in __restore_rt
[+]
─── Threads ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
[1] id 1174088 name postgres from 0x000055b7e4088b40 in AllocSetContextCreateInternal+0 at /home/rthompso/src/git/postgres/src/backend/utils/mmgr/aset.c:389
─── Variables ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
arg parent = 0x0, name = 0x55b7e416f179 "PgStat Shared Ref": 80 'P', minContextSize = 0, initBlockSize = 1024, maxBlockSize = 8192
loc firstBlockSize = <optimized out>, set = <optimized out>, block = <optimized out>, __FUNCTION__ = "AllocSetContextCreateInternal", __func__ = "AllocSetContextCreateInternal"
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────$4 = 1print CacheMemoryContext == NULL$5 = (MemoryContext) 0x0print parent
Thanks,
Reid
Codes seem good, my question is:
Do auto vacuum processes need CacheMemoryContext?
Is it designed not to create CacheMemoryContext in such processes?
If so, we’d better use TopMemoryContext in such processes.
Regards,
Zhang Mingli
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