Re: Online verification of checksums

From: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
To: Michael Banck <michael(dot)banck(at)credativ(dot)de>
Cc: Stephen Frost <sfrost(at)snowman(dot)net>, Michael Paquier <michael(at)paquier(dot)xyz>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>
Subject: Re: Online verification of checksums
Date: 2019-03-28 17:19:05
Message-ID: 20190328171905.GA16397@development
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On Thu, Mar 28, 2019 at 05:08:33PM +0100, Michael Banck wrote:
>I have rebased this patch now.
>I also fixed the two issues Andres reported, namely a zeroed-out
>pageheader and a random LSN. The first is caught be checking for an all-
>zero-page in the way PageIsVerified() does. The second is caught by
>comparing the upper 32 bits of the LSN as well and demanding that they
>are equal. If the LSN is corrupted, the upper 32 bits should be wildly
>different to the current checkpoint LSN.
>Well, at least that is a stab at a fix; there is a window where the
>upper 32 bits could legitimately be different. In order to make that as
>small as possible, I update the checkpoint LSN every once in a while.

Doesn't that mean we'll report a false positive?


Tomas Vondra
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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