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In-Reply-To: <E30A005D-0CD4-40E2-8865-B1AC85A1AD71@yesql.se>
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Thu, 27 Apr 2023 10:53:01 -0400
Message-ID: <CAAKRu_Z8+UqT8D=k-bVuE8525Z3ri4_xfCuOVnuQ-5yWc+tUew@mail.gmail.com>
Subject: Re: Should vacuum process config file reload more often
To: Daniel Gustafsson <daniel@yesql.se>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, John Naylor <john.naylor@enterprisedb.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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On Thu, Apr 27, 2023 at 8:55=E2=80=AFAM Daniel Gustafsson <daniel@yesql.se>=
 wrote:
>
> > On 27 Apr 2023, at 14:10, Masahiko Sawada <sawada.mshk@gmail.com> wrote=
:
> >
> > On Thu, Apr 27, 2023 at 6:30=E2=80=AFPM John Naylor
> > <john.naylor@enterprisedb.com> wrote:
> >>
> >>
> >> On Fri, Apr 7, 2023 at 6:08=E2=80=AFAM Daniel Gustafsson <daniel@yesql=
.se> wrote:
> >>>
> >>> 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 th=
e quick
> >>> turnaround times on reviews in this thread!
> >>
> >> -       VacuumFailsafeActive =3D false;
> >> +       Assert(!VacuumFailsafeActive);
> >>
> >> I can trigger this assert added in commit 7d71d3dd08.
> >>
> >> First build with the patch in [1], then:
> >>
> >> session 1:
> >>
> >> CREATE EXTENSION xid_wraparound ;
> >>
> >> CREATE TABLE autovacuum_disabled(id serial primary key, data text) WIT=
H (autovacuum_enabled=3Dfalse);
> >> INSERT INTO autovacuum_disabled(data) SELECT generate_series(1,1000);
> >>
> >> -- I can trigger without this, but just make sure it doesn't get vacuu=
med
> >> BEGIN;
> >> DELETE FROM autovacuum_disabled WHERE id % 2 =3D 0;
> >>
> >> session 2:
> >>
> >> -- 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;
> >>
> >> VACUUM autovacuum_disabled;
> >>
> >> 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.aut=
ovacuum_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_m=
em" 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
> >>
> >> #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 "!VacuumFailsafeActi=
ve",
> >>    fileName=3DfileName@entry=3D0xa4da38 "../src/backend/access/heap/va=
cuumlazy.c", lineNumber=3DlineNumber@entry=3D392) at ../src/backend/utils/e=
rror/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@ent=
ry=3Dtrue,
> >>    bstrategy=3Dbstrategy@entry=3D0x14ddca8)
> >>    at ../src/backend/commands/vacuum.c:2202
> >> #7  0x000000000069b0e4 in vacuum_rel (relid=3D16398, relation=3D<optim=
ized out>,
> >>    params=3Dparams@entry=3D0x7ffec2858850, skip_privs=3Dskip_privs@ent=
ry=3Dfalse,
> >>    bstrategy=3Dbstrategy@entry=3D0x14ddca8)
> >>    at ../src/backend/commands/vacuum.c:2236
> >
> > 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 a=
nd 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 lookin=
g and
> testing but I'm fairly sure this is the right fix, so unless I find somet=
hing
> else I will go ahead with this.
>
> xid_wraparound is a really nifty testing tool. Very cool.Makes sense to m=
e too.

Fix LGTM.
Though we previously set it to false before this series of patches,
perhaps it is
worth adding a comment about why VacuumFailsafeActive must be reset here
even though we reset it before vacuuming each table?

- Melanie