Re: Enabling Checksums

From: Markus Wanner <markus(at)bluegap(dot)ch>
To: Craig Ringer <craig(at)2ndQuadrant(dot)com>
Cc: Jeff Davis <pgsql(at)j-davis(dot)com>, Jesper Krogh <jesper(at)krogh(dot)cc>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Enabling Checksums
Date: 2012-11-12 10:13:43
Message-ID: 50A0CBD7.8070906@bluegap.ch
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On 11/12/2012 10:44 AM, Craig Ringer wrote:
> That'll make it hard for VACUUM, hint-bit setting, etc to
> opportunistically checksum pages whenever they're doing a page write anyway.

It *is* a hard problem, yes. And the single bit doesn't really solve it.
So I'm arguing against opportunistically checksumming in general. Who
needs that anyway?

> Is it absurd to suggest using another bitmap, like the FSM or visibility
> map, to store information on page checksumming while checksumming is
> enabled but incomplete?

Not absurd. But arguably inefficient, because that bitmap may well
become a bottleneck itself. Plus there's the problem of making sure
those pages are safe against corruptions, so you'd need to checksum the
checksum bitmap... doesn't sound like a nice solution to me.

This has certainly been discussed before.

Regards

Markus Wanner

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