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Subject: Re: Should vacuum process config file reload more often
From: Daniel Gustafsson <daniel@yesql.se>
In-Reply-To: <CAD21AoB_NQwdznBqcTMPv=vx71feDvBTNEMAvaUMAGqNcruk9Q@mail.gmail.com>
Date: Thu, 27 Apr 2023 14:54:57 +0200
Cc: John Naylor <john.naylor@enterprisedb.com>,
 Melanie Plageman <melanieplageman@gmail.com>,
 Robert Haas <robertmhaas@gmail.com>,
 Andres Freund <andres@anarazel.de>,
 Tom Lane <tgl@sss.pgh.pa.us>,
 Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
 Amit Kapila <amit.kapila16@gmail.com>
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To: Masahiko Sawada <sawada.mshk@gmail.com>
Archived-At: <https://www.postgresql.org/message-id/E30A005D-0CD4-40E2-8865-B1AC85A1AD71%40yesql.se>
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> On 27 Apr 2023, at 14:10, Masahiko Sawada <sawada.mshk@gmail.com> =
wrote:
>=20
> On Thu, Apr 27, 2023 at 6:30=E2=80=AFPM John Naylor
> <john.naylor@enterprisedb.com> wrote:
>>=20
>>=20
>> On Fri, Apr 7, 2023 at 6:08=E2=80=AFAM Daniel Gustafsson =
<daniel@yesql.se> wrote:
>>>=20
>>> I had another read-through and test-through of this version, and =
have applied
>>> it with some minor changes to comments and whitespace.  Thanks for =
the quick
>>> turnaround times on reviews in this thread!
>>=20
>> -       VacuumFailsafeActive =3D false;
>> +       Assert(!VacuumFailsafeActive);
>>=20
>> I can trigger this assert added in commit 7d71d3dd08.
>>=20
>> First build with the patch in [1], then:
>>=20
>> session 1:
>>=20
>> CREATE EXTENSION xid_wraparound ;
>>=20
>> CREATE TABLE autovacuum_disabled(id serial primary key, data text) =
WITH (autovacuum_enabled=3Dfalse);
>> INSERT INTO autovacuum_disabled(data) SELECT generate_series(1,1000);
>>=20
>> -- I can trigger without this, but just make sure it doesn't get =
vacuumed
>> BEGIN;
>> DELETE FROM autovacuum_disabled WHERE id % 2 =3D 0;
>>=20
>> session 2:
>>=20
>> -- get to failsafe limit
>> SELECT consume_xids(1*1000*1000*1000);
>> INSERT INTO autovacuum_disabled(data) SELECT 1;
>> SELECT consume_xids(1*1000*1000*1000);
>> INSERT INTO autovacuum_disabled(data) SELECT 1;
>>=20
>> VACUUM autovacuum_disabled;
>>=20
>> WARNING:  cutoff for removing and freezing tuples is far in the past
>> HINT:  Close open transactions soon to avoid wraparound problems.
>> You might also need to commit or roll back old prepared transactions, =
or drop stale replication slots.
>> WARNING:  bypassing nonessential maintenance of table =
"john.public.autovacuum_disabled" as a failsafe after 0 index scans
>> DETAIL:  The table's relfrozenxid or relminmxid is too far in the =
past.
>> HINT:  Consider increasing configuration parameter =
"maintenance_work_mem" or "autovacuum_work_mem".
>> You might also need to consider other ways for VACUUM to keep up with =
the allocation of transaction IDs.
>> server closed the connection unexpectedly
>>=20
>> #0  0x00007ff31f68ebec in __pthread_kill_implementation ()
>>   from /lib64/libc.so.6
>> #1  0x00007ff31f63e956 in raise () from /lib64/libc.so.6
>> #2  0x00007ff31f6287f4 in abort () from /lib64/libc.so.6
>> #3  0x0000000000978032 in ExceptionalCondition (
>>    conditionName=3DconditionName@entry=3D0xa4e970 =
"!VacuumFailsafeActive",
>>    fileName=3DfileName@entry=3D0xa4da38 =
"../src/backend/access/heap/vacuumlazy.c", =
lineNumber=3DlineNumber@entry=3D392) at =
../src/backend/utils/error/assert.c:66
>> #4  0x000000000058c598 in heap_vacuum_rel (rel=3D0x7ff31d8a97d0,
>>    params=3D<optimized out>, bstrategy=3D<optimized out>)
>>    at ../src/backend/access/heap/vacuumlazy.c:392
>> #5  0x000000000069af1f in table_relation_vacuum (bstrategy=3D0x14ddca8,=

>>    params=3D0x7ffec28585f0, rel=3D0x7ff31d8a97d0)
>>    at ../src/include/access/tableam.h:1705
>> #6  vacuum_rel (relid=3Drelid@entry=3D16402, =
relation=3Drelation@entry=3D0x0,
>>    params=3Dparams@entry=3D0x7ffec28585f0, =
skip_privs=3Dskip_privs@entry=3Dtrue,
>>    bstrategy=3Dbstrategy@entry=3D0x14ddca8)
>>    at ../src/backend/commands/vacuum.c:2202
>> #7  0x000000000069b0e4 in vacuum_rel (relid=3D16398, =
relation=3D<optimized out>,
>>    params=3Dparams@entry=3D0x7ffec2858850, =
skip_privs=3Dskip_privs@entry=3Dfalse,
>>    bstrategy=3Dbstrategy@entry=3D0x14ddca8)
>>    at ../src/backend/commands/vacuum.c:2236
>=20
> Good catch. I think the problem is that vacuum_rel() is called
> recursively and we don't reset VacuumFailsafeActive before vacuuming
> the toast table. I think we should reset it in heap_vacuum_rel()
> instead of Assert(). It's possible that we trigger the failsafe mode
> only for either one.Please find the attached patch.

Agreed, that matches my research and testing, I have the same diff here =
and it
passes testing and works as intended.  This was briefly discussed in [0] =
and
slightly upthread from there but then missed.  I will do some more =
looking and
testing but I'm fairly sure this is the right fix, so unless I find =
something
else I will go ahead with this.

xid_wraparound is a really nifty testing tool. Very cool.

--
Daniel Gustafsson

[0] CAAKRu_b1HjGCTsFpUnmwLNS8NeXJ+JnrDLhT1osP+Gq9HCU+Rw@mail.gmail.com=