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help / color / mirror / Atom feedFrom: Antonin Houska <ah@cybertec.at>
To: alvherre@kurilemu.de
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Race conditions in logical decoding
Date: Fri, 23 Jan 2026 07:33:32 +0100
Message-ID: <3805.1769150012@localhost> (raw)
In-Reply-To: <202601221950.c5lwdnye3idv@alvherre.pgsql>
References: <202601221950.c5lwdnye3idv@alvherre.pgsql>
Álvaro Herrera <alvherre@kurilemu.de> wrote:
> I think this algorithm is strange -- if you do have to wait more than
> once for one transaction, it would lead to doing the
> TransactionIdDidCommit again times for _all_ transactions by starting
> the inner loop from scratch, which sounds really wasteful. Why not nest
> the for() loops the other way around?
I'm quite sure I wanted to iterate through committed.xnt in the outer loop,
but probably got distracted by something else and messed things up.
> Something like this perhaps,
>
> for (int i = 0; i < builder->committed.xcnt; i++)
> {
> for (;;)
> {
> if (TransactionIdDidCommit(builder->committed.xip[i]))
> break;
> else
> {
> (void) WaitLatch(MyLatch,
> WL_LATCH_SET, WL_TIMEOUT, WL_EXIT_ON_PM_DEATH,
> 10L,
> WAIT_EVENT_SNAPBUILD_CLOG);
> ResetLatch(MyLatch);
> }
> CHECK_FOR_INTERRUPTS();
> }
> }
>
> This way you wait repeatedly for one transaction until it is marked
> committed; and once it does, you don't test it again.
Sure, that's much beter. Thanks.
--
Antonin Houska
Web: https://www.cybertec-postgresql.com
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To: pgsql-hackers@postgresql.org
Cc: ah@cybertec.at, alvherre@kurilemu.de, pgsql-hackers@lists.postgresql.org
Subject: Re: Race conditions in logical decoding
In-Reply-To: <3805.1769150012@localhost>
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