Horton

Re: Offline enabling/disabling of data checksums

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Michael Banck <michael.banck@credativ.de>
Cc: Magnus Hagander <magnus@hagander.net>, Fabien COELHO <coelho@cri.ensmp.fr>, Sergei Kornilov <sk@zsrv.org>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2019-03-15T02:50:27Z
Lists: pgsql-hackers

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On Thu, Mar 14, 2019 at 04:26:20PM +0100, Michael Banck wrote:
> Am Donnerstag, den 14.03.2019, 15:26 +0100 schrieb Magnus Hagander:
>> One big-hammer method could be similar to what pg_upgrade does --
>> temporarily rename away the controlfile so postgresql can't start, and
>> when done, put it back.
> 
> That sounds like a good solution to me. I've made PoC patch for that,
> see attached.

Indeed.  I did not know this trick from pg_upgrade.  We could just use
the same.

> The only question is whether pg_checksums should try to move pg_control
> back (i) on failure (ii) when interrupted?

Yes, we should have a callback on SIGINT and SIGTERM here which just
moves back in place the control file if the temporary one exists.  I
have been able to grab some time to incorporate the feedback gathered
on this thread, and please find attached a new version of the patch to
add --enable/--disable.  The main changes are:
- When enabling checksums, fsync first the data directory, and at the
end then update/flush the control file and its parent folder as Fabien
has reported.
- When disabling checksums, only work on the control file, as Fabien
has also reported.
- Rename the control file when beginning the enabling operation, with
a callback to rename the file back if the operation is interrupted.

Does this make sense?
--
Michael

Commits

  1. Reorganize Notes section in documentation of pg_checksums

  2. Add option -N/--no-sync to pg_checksums

  3. Add options to enable and disable checksums in pg_checksums

  4. Refactor more code logic to update the control file

  5. Rename pg_verify_checksums to pg_checksums

  6. Fix cross-version compatibility checks of pg_verify_checksums

  7. Add routine able to update the control file to src/common/