Re: Incorrect visibility test function assigned to snapshot

Alvaro Herrera <alvherre(at)2ndquadrant(dot)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
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