| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, david(at)fetter(dot)org, aidan(at)highrise(dot)ca, stark(at)mit(dot)edu, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: 16-bit page checksums for 9.2 |
| Date: | 2012-01-06 19:35:01 |
| Message-ID: | 201201062035.02995.andres@anarazel.de |
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| Lists: | pgsql-hackers |
On Friday, January 06, 2012 07:26:14 PM Simon Riggs wrote:
> The following patch (v4) introduces a new WAL record type that writes
> backup blocks for the first hint on a block in any checkpoint that has
> not previously been changed. IMHO this fixes the torn page problem
> correctly, though at some additional loss of performance but not the
> total catastrophe some people had imagined. Specifically we don't need
> to log anywhere near 100% of hint bit settings, much more like 20-30%
> (estimated not measured).
Well, but it will hurt in those cases where hint bits already hurt hugely.
Which is for example when accessing huge amounts of data the first time after
loading it. Which is not exactly uncommon...
Andres
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