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From: Paul Allen <paulcrtool@gmail.com>
Date: Thu, 20 Mar 2025 16:45:39 +0400
Message-ID: <CAExgkpfsx=u-X64FFcSfgNhDzhhTXJDhE4WeuS+ZvRHGvwNx2w@mail.gmail.com>
Subject: Re: Bloated toast table with empty associated table
To: Ron Johnson <ronljohnsonjr@gmail.com>
Cc: "pgsql-generallists.postgresql.org" <pgsql-general@lists.postgresql.org>
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> It's the general principle that the _scale_factor defaults are in my expe=
rience too high.
Sorry, didn't mentioned

Ok, thanks, I will use the cron task.

It's toast behaviour still seems odd to me. Is there a way to prevent
this behaviour at all, to not store rows which were failed to insert?

On Thu, Mar 20, 2025 at 4:28=E2=80=AFPM Ron Johnson <ronljohnsonjr@gmail.co=
m> wrote:
>
> On Thu, Mar 20, 2025 at 8:22=E2=80=AFAM Paul Allen <paulcrtool@gmail.com>=
 wrote:
>>
>> > Instantaneously and repeatedly, while ignoring the error?
>> Yes, that's how it should work and I probably can't do anything about it=
.
>>
>> > Your _scale_factor values are too high.  Drop them down to about 5%.
>>
>> Okay, but what about altering controlzone_passage table, where I set
>> all _scale_factor
>> values to 0? If this did not have an effect, then how will the value
>> of 5% affect? Maybe I
>> misunderstand, but the table does not change by any number of rows and
>> its logical size
>> remains zero. Anyway I will try it.
>
>
> It's the general principle that the _scale_factor defaults are in my expe=
rience too high.
>
> Like I said: "That's not the proximate cause, though" of this table's blo=
at.
>
>>
>> > I'd create a cron entry that does a regular "vacuumdb -d the_db -t  co=
ntrolzone_passage".  How often you run it depends on how quickly it bloats.
>>
>> Seems like it is the only solution for now.
>
>
> The autovacuum daemon can't know/see everything.
>
>>
>> On Thu, Mar 20, 2025 at 4:03=E2=80=AFPM Ron Johnson <ronljohnsonjr@gmail=
.com> wrote:
>> >
>> > On Thu, Mar 20, 2025 at 7:40=E2=80=AFAM Paul Allen <paulcrtool@gmail.c=
om> wrote:
>> >>
>> >> Hello.
>> >>
>> >> Preconditions.
>> >>
>> >> I have some empty table and constantly try to execute `insert ... on
>> >> conflict do update ...` on it. My data in row which I try to insert i=
s
>> >> invalid by violation of foreing key constraint, so I am getting error
>> >> while inserting and table keeps being empty. This table have some byt=
ea
>> >> columns with default storage type. It's purpose is to keep images.
>> >> PostgreSQL version is 15, everything is default, autovacuum settings =
is
>> >>
>> >> ```
>> >> autovacuum  on
>> >> autovacuum_analyze_scale_factor  0.1
>> >> autovacuum_analyze_threshold  50
>> >> autovacuum_freeze_max_age  200000000
>> >> autovacuum_max_workers  3
>> >> autovacuum_multixact_freeze_max_age  400000000
>> >> autovacuum_naptime  60
>> >> autovacuum_vacuum_cost_delay  20
>> >> autovacuum_vacuum_cost_limit  -1
>> >> autovacuum_vacuum_scale_factor  0.2
>> >> autovacuum_vacuum_threshold  50
>> >> autovacuum_work_mem  -1
>> >> log_autovacuum_min_duration  -1
>> >
>> >
>> > Your _scale_factor values are too high.  Drop them down to about 5%.
>> >
>> > That's not the proximate cause, though.
>> >
>> >>
>> >> ```
>> >>
>> >> Problem.
>> >>
>> >> My backend application attempts unsuccessfully repeatedly to insert t=
he
>> >> same ~100 rows with images,
>> >
>> >
>> > Instantaneously and repeatedly, while ignoring the error?
>> >
>> >>
>> >> and despite table's row count remains 0,
>> >> toast table's size is growing up permanently, reaching 100, 200, 300 =
GB
>> >> until it takes all available space.
>> >>
>> >> VACUUM FULL fixes this, but a want some automatic solution. I tried t=
o
>> >> alter table, believing that the settings below would force autovacuum=
 to
>> >> clean toast anyway, but it had no effect.
>> >>
>> >> ```
>> >> alter table controlzone_passage set (
>> >> autovacuum_enabled =3D true,
>> >> toast.autovacuum_enabled =3D true,
>> >> autovacuum_vacuum_threshold =3D 0,
>> >> toast.autovacuum_vacuum_threshold =3D 0,
>> >> autovacuum_vacuum_scale_factor =3D 0,
>> >> toast.autovacuum_vacuum_scale_factor =3D 0,
>> >> autovacuum_analyze_threshold =3D 0,
>> >> autovacuum_analyze_scale_factor =3D 0);
>> >> ```
>> >>
>> >> At the moment, my assumption is that the autovacuum is not working
>> >> because the number of rows in the table does not change and remains
>> >> zero. Any solution will suit me, for example, not to write rows to to=
ast
>> >> if their insertion failed. Or the proper setting of the autovacuum.
>> >> Please tell me what can be done.
>> >
>> >
>> > I'd create a cron entry that does a regular "vacuumdb -d the_db -t  co=
ntrolzone_passage".  How often you run it depends on how quickly it bloats.
>> >
>> > --
>> > Death to <Redacted>, and butter sauce.
>> > Don't boil me, I'm still alive.
>> > <Redacted> lobster!
>
>
>
> --
> Death to <Redacted>, and butter sauce.
> Don't boil me, I'm still alive.
> <Redacted> lobster!