From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Magnus Hagander <magnus(at)hagander(dot)net> |
Cc: | Andres Freund <andres(at)anarazel(dot)de>, Michael Banck <michael(dot)banck(at)credativ(dot)de>, David Steele <david(at)pgmasters(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, pgsql-committers(at)lists(dot)postgresql(dot)org |
Subject: | Re: pgsql: Validate page level checksums in base backups |
Date: | 2018-04-03 18:55:07 |
Message-ID: | 23574.1522781707@sss.pgh.pa.us |
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Magnus Hagander <magnus(at)hagander(dot)net> writes:
> On Tue, Apr 3, 2018 at 8:29 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> It's scribbling on the source cluster's disk files and assuming that that
>> translates one-for-one to what gets sent to the slave server --- but what
>> if some of the blocks that it modifies on-disk are resident in the
>> source's shared buffers? I think you'd have to shut down the source and
>> then apply the corruption if you want stable results.
> It doesn't actually use a slave server as part of the tests.
> And basebackups don't read from the sources shared buffers, but it *does*
> read from the kernel buffers.
Right, so the failure case occurs when the source server writes back a
dirty page from its shared buffers to disk, in between the test script's
corrupting that page on-disk and then trying to read it.
Again, you'd have several orders of magnitude better chance of getting
reproducible behavior if you were targeting something that wasn't a
system catalog.
regards, tom lane
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