| 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: | 2011-12-28 09:22:14 |
| Message-ID: | CA+U5nMJhRbkmNqVWCJTvCLfDcFJNu0j-H_XGZzv7=P0Uamfnsg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Dec 28, 2011 at 7:42 AM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>> How would you know when to look in the double write buffer?
>
>
> You scan the double-write buffer, and every page in the double write buffer
> that has a valid checksum, you copy to the main storage. There's no need to
> check validity of pages in the main storage.
OK, then we are talking at cross purposes. Double write buffers, in
the way you explain them allow us to remove full page writes. They
clearly don't do anything to check page validity on read. Torn pages
are not the only fault we wish to correct against... and the double
writes idea is orthogonal to the idea of checksums.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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