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Re: 16-bit page checksums for 9.2

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Aidan Van Dyk <aidan(at)highrise(dot)ca>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: 16-bit page checksums for 9.2
Date: 2011-12-24 16:06:59
Message-ID: CA+U5nMLPdODfPNMCFcHGG_t7TiMc-2pZocjoRCZMdcDF0Ya1vA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Sat, Dec 24, 2011 at 3:51 PM, Aidan Van Dyk <aidan(at)highrise(dot)ca> wrote:

> Not an expert here, but after reading through the patch quickly, I
> don't see anything that changes the torn-page problem though, right?
>
> Hint bits aren't wal-logged, and FPW isn't forced on the hint-bit-only
> dirty, right?

Checksums merely detect a problem, whereas FPWs correct a problem if
it happens, but only in crash situations.

So this does nothing to remove the need for FPWs, though checksum
detection could be used for double write buffers also.

Checksums work even when there is no crash, so if your disk goes bad
and corrupts data then you'll know about it as soon as it happens.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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Subject: Re: 16-bit page checksums for 9.2
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Subject: Re: 16-bit page checksums for 9.2

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