| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Jeff Davis <pgsql(at)j-davis(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Simon Riggs <simon(at)2ndQuadrant(dot)com>, Ants Aasma <ants(at)cybertec(dot)at>, Greg Smith <greg(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Enabling Checksums |
| Date: | 2013-04-13 13:29:30 |
| Message-ID: | 20130413132930.GA10556@awork2.anarazel.de |
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| Thread: | |
| Lists: | pgsql-hackers |
On 2013-04-13 09:14:26 -0400, Bruce Momjian wrote:
> On Fri, Apr 12, 2013 at 02:38:27PM -0700, Jeff Davis wrote:
> > In general, we have more flexibility with WAL because there is no
> > upgrade issue. It would be nice to share code with the data page
> > checksum algorithm; but really we should just use whatever offers the
> > best trade-off in terms of complexity, performance, and error detection
> > rate.
> >
> > I don't think we need to decide all of this right now. Personally, I'm
> > satisfied having SIMD checksums on data pages now and leaving WAL
> > optimization until later.
>
> As I understand it, SIMD is just a CPU-optimized method for producing a
> CRC checksum. Is that right? Does it produce the same result as a
> non-CPU-optimized CRC calculation?
No we are talking about a different algorithm that results in different
results, thats why its important to choose now since we can't change it
later without breaking pg_upgrade in further releases.
http://en.wikipedia.org/wiki/SIMD_%28hash_function%29
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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