| From: | Abhijit Menon-Sen <ams(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Subject: | Re: What exactly is our CRC algorithm? |
| Date: | 2014-12-26 18:22:41 |
| Message-ID: | 20141226182241.GA31313@toroid.org |
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| Lists: | pgsql-hackers |
At 2014-12-26 13:11:43 -0500, bruce(at)momjian(dot)us wrote:
>
> Is this something that could potentially change the data stored on
> disk? Does pg_upgrade need to check for changes in this area? Is the
> detection exposed by pg_controldata? Could this affect running the
> data directory on a different CPU?
No to all.
Subsequent to Heikki's change (already in master) to use the CRC-32C
algorithm (instead of the earlier mistakenly-reflected-but-not-quite
one), both the slice-by-8 software implementation posted earlier and
the SSE4.2 CRC32* instructions will compute exactly the same value.
(Yes, I have verified this in both cases.)
-- Abhijit
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