Horton

Re: archive modules

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, bharath.rupireddyforpostgres@gmail.com, tgl@sss.pgh.pa.us, peter.eisentraut@enterprisedb.com, benoit.lobreau@gmail.com, alvherre@alvh.no-ip.org, robertmhaas@gmail.com, bossartn@amazon.com, david@pgmasters.net, masao.fujii@oss.nttdata.com, pgsql-hackers@postgresql.org, magnus@hagander.net, sfrost@snowman.net
Date: 2022-11-05T21:08:58Z
Lists: pgsql-hackers 
On Mon, Oct 17, 2022 at 02:49:51PM +0900, Michael Paquier wrote:
> And, by the way, this patch would prevent the existence of archive
> modules that need to be loaded but *want* an archive_command with
> what they want to achieve.  That does not strike me as a good idea if
> we want to have a maximum of flexibility with this facility.

Such a module could define a custom GUC that accepts a shell command.  I
don't think we should overload the meaning of archive_command based on the
whims of whatever archive module is loaded.  Besides the potential end-user
confusion, your archive_command might be unexpectedly used incorrectly if
you forget to set archive_library.

Perhaps we could eventually move the archive_command functionality to a
contrib module (i.e., "shell_archive") so that users must always set
archive_library.  But until then, I suspect it's better to treat modules
and commands as two separate interfaces to ease migration from older major
versions (even though archive_command is now essentially a built-in archive
module).

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

Commits

  1. Disallow setting archive_library and archive_command at the same time

  2. Restore archive_command documentation

  3. Doc: improve explanation of when custom GUCs appear in pg_settings.

  4. doc: Add note about re-archiving of same WAL files in docs.

  5. In basic_archive tests, insist on wal_level='replica'.

  6. Allow archiving via loadable modules.

  7. Move the code to archive files via the shell to a separate file.