Re: [HACKERS] CIC and deadlocks

On 4/11/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

>
> [ itch... ] The problem is with time-extended execution of
> GetSnapshotData; what happens if the other guy lost the CPU for a good
> long time while in the middle of GetSnapshotData? He might set his
> xmin based on info you saw as long gone.
>
> You might be correct that it's safe, but the argument would have to
> hinge on the OldestXmin process being unable to commit because of
> someone holding shared ProcArrayLock; a point you are definitely not
> making above. (Study the comments in GetSnapshotData for awhile,
> also those in xact.c's commit-related code.)
>
>
My argument was based on what you said above, but I obviously did not
state it well :)

Anyways, I think its better to be safe and we agree that its not such a
bad thing to take exclusive lock on procarray because CIC is not something
that happens very often. Attached is a revised patch which takes exclusive
lock on the procarray, rest remaining the same.

Thanks,
Pavan

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