Horton

Re: BF mamba failure

Alexander Law <exclusion@gmail.com>

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From: Alexander Lakhin <exclusion@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, Amit Kapila <amit.kapila16@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Peter Smith <smithpb2250@gmail.com>
Date: 2023-03-18T15:00:01Z
Lists: pgsql-hackers

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Hi,

18.03.2023 07:26, Tom Lane wrote:
> Amit Kapila<amit.kapila16@gmail.com>  writes:
>> Peter Smith has recently reported a BF failure [1]. AFAICS, the call
>> stack of failure [2] is as follows:
> Note the assertion report a few lines further up:
>
> TRAP: failed Assert("pg_atomic_read_u32(&entry_ref->shared_entry->refcount) == 0"), File: "pgstat_shmem.c", Line: 560, PID: 25004

This assertion failure can be reproduced easily with the attached patch:
============== running regression test queries        ==============
test oldest_xmin                  ... ok           55 ms
test oldest_xmin                  ... FAILED (test process exited with exit code 1)      107 ms
test oldest_xmin                  ... FAILED (test process exited with exit code 1)        8 ms
============== shutting down postmaster               ==============

contrib/test_decoding/output_iso/log/postmaster.log contains:
TRAP: failed Assert("pg_atomic_read_u32(&entry_ref->shared_entry->refcount) == 0"), File: "pgstat_shmem.c", Line: 561, 
PID: 456844

With the sleep placed above Assert(entry_ref->shared_entry->dropped) this Assert fails too.

Best regards,
Alexander

Commits

  1. Add information about "generation" when dropping twice pgstats entry

  2. Fix race conditions with drop of reused pgstats entries