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From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: postgresql@taljaren.se, pgsql-hackers@lists.postgresql.org, Michael Paquier <michael@paquier.xyz>
Subject: Re: BUG #17717: Regression in vacuumdb (15 is slower than 10/11 and possible memory issue)
Date: Wed, 28 Dec 2022 13:23:21 -0800
Message-ID: <20221228212321.GB4009813@nathanxps13> (raw)
In-Reply-To: <419503.1672262419@sss.pgh.pa.us>
References: <17717-6c50eb1c7d23a886@postgresql.org>
	<3439037.1671130590@sss.pgh.pa.us>
	<CAH2-Wzne4Wgaaruq-VSY2qWNhxcPRqWUbdwVQPkM81TpaHY_kQ@mail.gmail.com>
	<3544447.1671141436@sss.pgh.pa.us>
	<CAH2-WzkXmYt-K+pQqMqjFgwU7jiykD3amngd5-jkqQF=gST7Og@mail.gmail.com>
	<3672943.1671202149@sss.pgh.pa.us>
	<CAH2-WzkHRxcE-0Mub9N0Rr09SGEEF1Ex4pUbcOBSRoNGNVy93w@mail.gmail.com>
	<407579.1672258403@sss.pgh.pa.us>
	<20221228211253.GA4009571@nathanxps13>
	<419503.1672262419@sss.pgh.pa.us>

On Wed, Dec 28, 2022 at 04:20:19PM -0500, Tom Lane wrote:
> Nathan Bossart <nathandbossart@gmail.com> writes:
>> I think the main difference between your patch and mine is that I've
>> exposed vac_update_datfrozenxid() via a function instead of a VACUUM
>> option.  IMHO that feels a little more natural, but I can't say I feel too
>> strongly about it.
> 
> I thought about that but it seems fairly unsafe, because that means
> that vac_update_datfrozenxid is executing inside a user-controlled
> transaction.  I don't think it will hurt us if the user does a
> ROLLBACK afterward --- but if he sits on the open transaction,
> that would be bad, if only because we're still holding the
> LockDatabaseFrozenIds lock which will block other VACUUMs.
> There might be more hazards besides that; certainly no one has ever
> tried to run vac_update_datfrozenxid that way before.

That's a good point.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com





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