| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com>, Florian Pflug <fgp(at)phlo(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Kevin Grittner <kgrittn(at)ymail(dot)com>, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Greg Stark <stark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [PATCH] Negative Transition Aggregate Functions (WIP) |
| Date: | 2014-01-16 19:23:47 |
| Message-ID: | 6870.1389900227@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> You'll have to handle adding negative values and underflow as
> well.
Right.
> Maybe it's instead sufficient to just have flag indicating that you're
> working with a state that hasn't overflowed so far and just plain int8
> math as long as that's the case, and entirely fall back to the current
> path once overflowed. That will probably be slightly faster and easily
> handle the majority of cases since overflowing int8 ought to be pretty
> rare in the real world.
Dunno, I think that a transition state containing both an int64 and
a (presumably separately palloc'd) numeric will be a real PITA.
And it will not be faster, because the principal drag on performance
will just be the overflow test, which you have to do either way.
regards, tom lane
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