Re: Phantom command ids again

Heikki Linnakangas <heikki@enterprisedb.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