| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
| Cc: | 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 18:59:00 |
| Message-ID: | 32025.1389898740@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> writes:
> I propose that we reimplement sum(bigint) in a more efficient way: For
> the internal state, let's use an int8 and a numeric overflow field. The
> transition function adds to the int8 variable, and checks for overflow.
> On overflow, increment the numeric field by one. In the final function,
> multiply the numeric by 2^64, and add the residual int8 value.
It'd probably be sufficient to handle it as two int64 fields (handmade
128-bit arithmetic, or maybe even not so handmade if that ever gets
reasonably common among C compilers). You're assuming the final output
is still numeric, right?
regards, tom lane
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