From: Antonin Houska <ah@cybertec.at>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Incorrect visibility test function assigned to snapshot
Date: Wed, 30 May 2018 15:45:32 +0200
Message-ID: <28218.1527687932@localhost> (raw)
In-Reply-To: <20180530132854.tkv37qiamepu3slh@alvherre.pgsql>
References: <20180530132854.tkv37qiamepu3slh@alvherre.pgsql>
Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> On 2018-May-30, Antonin Houska wrote:
>
> > In the header comment, SnapBuildInitialSnapshot() claims to set
> > snapshot->satisfies to the HeapTupleSatisfiesMVCC test function, and indeed it
> > converts the "xid" array to match its semantics (i.e. the xid items eventually
> > represent running transactions as opposed to the committed ones). However the
> > test function remains HeapTupleSatisfiesHistoricMVCC as set by
> > SnapBuildBuildSnapshot().
>
> Interesting. While this sounds like an oversight that should have
> horrible consequences, it's seems not to because the current callers
> don't seem to care about the ->satisfies function. Are you able to come
> up with some scenario in which it causes an actual problem?
Right, the current callers in the core do not seem to use that function. I hit
the issue when doing and testing some changes in an extension (pg_squeeze).
--
Antonin Houska
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26, A-2700 Wiener Neustadt
Web: https://www.cybertec-postgresql.com
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To: pgsql-hackers@postgresql.org
Cc: ah@cybertec.at, alvherre@2ndquadrant.com
Subject: Re: Incorrect visibility test function assigned to snapshot
In-Reply-To: <28218.1527687932@localhost>
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