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help / color / mirror / Atom feedFrom: Tom Lane <[email protected]>
To: Thomas Munro <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: [email protected]
Subject: Re: odd buildfarm failure - "pg_ctl: control file appears to be corrupt"
Date: Wed, 23 Nov 2022 17:05:03 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+hUKGKr0TBwFMZ_BxcOps4_WDxhX5tS2D1Mwb1fAHyMKxo-UA@mail.gmail.com>
References: <[email protected]>
<CA+hUKGL9w0VhZ=ceMDjXgCXy1BC5VzjwXc-HetSxfNzvBLge3A@mail.gmail.com>
<CA+hUKGKr0TBwFMZ_BxcOps4_WDxhX5tS2D1Mwb1fAHyMKxo-UA@mail.gmail.com>
Thomas Munro <[email protected]> writes:
> On Wed, Nov 23, 2022 at 11:03 PM Thomas Munro <[email protected]> wrote:
>> I assume this is ext4. Presumably anything that reads the
>> controlfile, like pg_ctl, pg_checksums, pg_resetwal,
>> pg_control_system(), ... by reading without interlocking against
>> writes could see garbage. I have lost track of the versions and the
>> thread, but I worked out at some point by experimentation that this
>> only started relatively recently for concurrent read() and write(),
>> but always happened with concurrent pread() and pwrite(). The control
>> file uses the non-p variants which didn't mash old/new data like
>> grated cheese under concurrency due to some implementation detail, but
>> now does.
Ugh.
> As for what to do about it, some ideas:
> 2. Retry after a short time on checksum failure. The probability is
> already miniscule, and becomes pretty close to 0 if we read thrice
> 100ms apart.
> First thought is that 2 is appropriate level of complexity for this
> rare and stupid problem.
Yeah, I was thinking the same. A variant could be "repeat until
we see the same calculated checksum twice".
regards, tom lane
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Subject: Re: odd buildfarm failure - "pg_ctl: control file appears to be corrupt"
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