| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Cc: | Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, stark(at)mit(dot)edu, aidan(at)highrise(dot)ca, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: 16-bit page checksums for 9.2 |
| Date: | 2011-12-27 23:39:48 |
| Message-ID: | CA+U5nMJK89jFTKCmegnoKRShaSTamFs4RLr6Fyshu1R05htq4g@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Dec 27, 2011 at 8:05 PM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> On 25.12.2011 15:01, Kevin Grittner wrote:
>>
>> I don't believe that. Double-writing is a technique to avoid torn
>> pages, but it requires a checksum to work. This chicken-and-egg
>> problem requires the checksum to be implemented first.
>
>
> I don't think double-writes require checksums on the data pages themselves,
> just on the copies in the double-write buffers. In the double-write buffer,
> you'll need some extra information per-page anyway, like a relfilenode and
> block number that indicates which page it is in the buffer.
How would you know when to look in the double write buffer?
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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