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From: Amit Kapila <[email protected]>
To: SATYANARAYANA NARLAPURAM <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Álvaro Herrera <[email protected]>
Cc: Antonin Houska <[email protected]>
Subject: Re: Possible premature SNAPBUILD_CONSISTENT with DB-specific running_xacts
Date: Mon, 20 Apr 2026 11:34:17 +0530
Message-ID: <CAA4eK1+Y7qwvzSjeY=KWWLHw3wQNxD7ebr5FoWTuBOYpRGhc3A@mail.gmail.com> (raw)
In-Reply-To: <CAHg+QDcQak4jx_6X2_Ws98rzG=xBARLjqm_=56wTRUtNsY4DZQ@mail.gmail.com>
References: <CAHg+QDcQak4jx_6X2_Ws98rzG=xBARLjqm_=56wTRUtNsY4DZQ@mail.gmail.com>

On Mon, Apr 20, 2026 at 12:29 AM SATYANARAYANA NARLAPURAM
<[email protected]> wrote:
>
> A cluster-wide decoder must never have its snapshot-builder state changed
> by a database-specific running_xacts record. Adding a check to return it early.
> I think otherwise a cluster wide decoder can potentially go to
> SNAPSHOT_CONSISTENT state immediately even though transactions older
> than nextXid are still in progress on a different DB (not tracked by running_xact
> record). This race is now possible with cluster wide decoders and Repack
> concurrently run.
>

I think this has been discussed previously, see [1]. As per my
understanding, we are not in agreement for the need of this
db-specific handling in the snapbuilder, see [2][3]. So, adding more
improvements/fixes on top of it doesn't sound advisable.

[1] - https://www.postgresql.org/message-id/CAA4eK1KWDbBk4FgbbWdivQLrPPzR4zgvfnHK4WjWC78rbuRVbg%40mail.gma...
[2] - https://www.postgresql.org/message-id/cdgw4sbbfcgk6du3iv54r2dgiy4tfywoklbotlmj4irxavdcr3%40glxfw5jj2...
[3] - https://www.postgresql.org/message-id/pveffyxhnuurhb44uzqlwo3rkyzorkfh2rot7uwzlf2axhfvbp%407nrs2omys...

-- 
With Regards,
Amit Kapila.

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