Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> I was about to resubmit the phantom command ids patch for review, as I
> noticed a little problem.
> In fmgr.c in record_C_func, we cache the xmin and cmin, and later in
> lookup_C_func we check that they match to determine if the cached
> information is still valid. With phantom command ids, the cmin is not
> valid outside the inserting transaction, which makes it unusable for
> that purpose.
I think that actually that's just belt-and-suspenders programming;
it should be sufficient to compare tuple TID and xmin. AFAICS a single
transaction cannot fill the same TID twice, since VACUUM would never
dare remove a tuple entered by a still-in-progress transaction. So the
cmin check doesn't seem necessary.
regards, tom lane
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