Horton

Re: [Patch] pg_rewind: options to use restore_command from recovery.conf or command line

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Alexey Kondratov <a.kondratov@postgrespro.ru>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Andrey Borodin <x4mmm@yandex-team.ru>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, vladimirlesk@yandex-team.ru, Dmitriy Sarafannikov <dsarafan@yandex-team.ru>
Date: 2018-10-30T03:01:23Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Move frontend-side archive APIs from src/common/ to src/fe_utils/

  2. Add -c/--restore-target-wal to pg_rewind

  3. Move routine definitions of xlogarchive.c to a new header file

  4. Move routine building restore_command to src/common/

  5. Integrate recovery.conf into postgresql.conf

On Mon, Oct 29, 2018 at 12:09:21PM +0300, Alexey Kondratov wrote:
> Currently in the patch, with dry-run option (-n) pg_rewind only fetches
> missing WALs to be able to build file map, while doesn't touch any data
> files. So I guess it behaves exactly as you described and we do not need a
> separate tool.

Makes sense perhaps.  Fetching only WAL segments which are needed for
the file map is critical, as you don't want to spend bandwidth for
nothing.  Now, I look at your patch, and I can see things to complain
about, at least three at short glance:
- The TAP test added will fail on Windows.
- Simply copy-pasting RestoreArchivedWAL() from the backend code to
pg_rewind is not an acceptable option.  You don't care about %r either
in this case.
- Reusing the GUC parser is something I would avoid as well.  Not worth
the complexity.

Another thing I am wondering is: do we actually need something complex?
What we want to know is what data is necessary to build the file map, so
we could also add an option to pg_rewind which checks what segments are
necessary and lets the user know about them?  This also avoids the
security-related problems of manipulating a command at option-level.
This kind of options makes folks willing to use more sensitive data on
command line, which is not always a good idea...
--
Michael