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Subject: Re: q re removal/recycling of WAL files
From: Rui DeSousa <rui@crazybean.net>
In-Reply-To: <4B485D8E-9692-4009-8562-43BC0E54C975@elevated-dev.com>
Date: Wed, 3 Nov 2021 19:37:45 -0400
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> On Nov 3, 2021, at 6:24 PM, Scott Ribe <scott_ribe@elevated-dev.com> =
wrote:
>=20
> Let's say that there's a big update as part of a migration, and that =
update times out, and the migration utility retries it several times. =
(Context is that sequence happened through automated utility, and filled =
the disk, leading to an unfortunate series of events.)
>=20
> 1) At what point does WAL from the failed & rolled back operations "go =
away"? During the next checkpoint? During the checkpoint after =
completion of all other transactions which overlapped time-wise with the =
timing-out ones?
>=20

WAL file can=E2=80=99t be recycled until it is no longer needed; thus =
after a checkpoint and archived as well (if enabled).=20

> 2) Is there a chance that never-visible rows would be written into =
tables, bloating them?
>=20

Yes, changes would be recorded into the tables; however, they would not =
be visible if the transaction was rolled back or aborted.  A subsequent =
vacuum would remove those records and truncate the file to high water =
mark if possible.=