From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Alexander Lakhin <exclusion@gmail.com>
Cc: PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Subject: Re: BUG #17064: Parallel VACUUM operations cause the error "global/pg_filenode.map contains incorrect checksum"
Date: Tue, 22 Jun 2021 10:11:06 -0400
Message-ID: <1715251.1624371066@sss.pgh.pa.us> (raw)
In-Reply-To: <CA+hUKGJ98=MOjDCnMAC5gSpkzrrey=O+aEQJ1OY03C=cVtiwkA@mail.gmail.com>
References: <17064-bb0d7904ef72add3@postgresql.org>
<ac119d1e-05d1-f050-b92a-0a524d68b848@iki.fi>
<CA+hUKGJ98=MOjDCnMAC5gSpkzrrey=O+aEQJ1OY03C=cVtiwkA@mail.gmail.com>
Thomas Munro <thomas.munro@gmail.com> writes:
> Your analysis seems right to me. We have to worry about both things:
> atomicity of writes on power failure (assumed to be sector-level,
> hence our 512 byte struct -- all good), and atomicity of concurrent
> reads and writes (we can't assume anything at all, so r/w locking is
> the simplest way to get a consistent read). Shouldn't relmap_redo()
> also acquire the lock exclusively?
Shouldn't we instead file a kernel bug report? I seem to recall that
POSIX guarantees atomicity of these things up to some operation size.
Or is that just for pipe I/O?
If we can't assume atomicity of relmapper file I/O, I wonder about
pg_control as well. But on the whole, what I'm smelling is a moderately
recently introduced kernel bug. We've been doing this this way for
years and heard no previous reports.
regards, tom lane
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Cc: tgl@sss.pgh.pa.us, thomas.munro@gmail.com, hlinnaka@iki.fi, exclusion@gmail.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17064: Parallel VACUUM operations cause the error "global/pg_filenode.map contains incorrect checksum"
In-Reply-To: <1715251.1624371066@sss.pgh.pa.us>
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