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Message-ID: <696cacde-79d0-4897-93bc-68fa317a7eb4@aklaver.com>
Date: Thu, 8 May 2025 08:10:51 -0700
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Subject: Re: pg_rewind problem: cannot find WAL
To: Luca Ferrari <fluca1978@gmail.com>,
 Laurenz Albe <laurenz.albe@cybertec.at>
Cc: pgsql-general <pgsql-general@lists.postgresql.org>
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From: Adrian Klaver <adrian.klaver@aklaver.com>
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On 5/8/25 04:26, Luca Ferrari wrote:
> On Thu, May 8, 2025 at 8:54 AM Luca Ferrari <fluca1978@gmail.com> wrote:
>>
>> I've pgbackrest making backups, so I have an archive_command. I'm
>> going to see if putting a restore_command can fix the problem.
>>
> 
> But I'm facing a quite trivial problem: in ubuntu installation the
> configuration files are separated from the PGDATA.
> Apparently pg_rewind is trying to read postgresql.conf to get the
> restore_command, and I don't know how to specify the different
> location of the postgresql.conf (cannot specifcy -c as in postgres):
> 
> $ /usr/lib/postgresql/17/bin/pg_rewind -D /var/lib/postgresql/17/main
> --source-server="user=replica_fluca host=dev-psqlha3
> dbname=replica_fluca" -R -P --debug -c
> postgres: could not access the server configuration file
> "/var/lib/postgresql/17/main/postgresql.conf": No such file or
> directory
> no data was returned by command "/usr/lib/postgresql/17/bin/postgres
> -D /var/lib/postgresql/17/main -C restore_command"
> child process exited with exit code 2
> pg_rewind: error: could not read restore_command from target cluster
> 
> Any idea?

/usr/lib/postgresql/17/bin/pg_rewind  --help
pg_rewind resynchronizes a PostgreSQL cluster with another copy of the 
cluster.

Usage:
   pg_rewind [OPTION]...

Options:
   -c, --restore-target-wal       use "restore_command" in target 
configuration to
                                  retrieve WAL files from archives
   -D, --target-pgdata=DIRECTORY  existing data directory to modify
       --source-pgdata=DIRECTORY  source data directory to synchronize with
       --source-server=CONNSTR    source server to synchronize with
   -n, --dry-run                  stop before modifying anything
   -N, --no-sync                  do not wait for changes to be written
                                  safely to disk
   -P, --progress                 write progress messages
   -R, --write-recovery-conf      write configuration for replication
                                  (requires --source-server)
       --config-file=FILENAME     use specified main server configuration
                                  file when running target cluster
       --debug                    write a lot of debug messages
       --no-ensure-shutdown       do not automatically fix unclean shutdown
       --sync-method=METHOD       set method for syncing files to disk
   -V, --version                  output version information, then exit
   -?, --help                     show this help, then exit


So use --config-file=FILENAME?

> Clearly, postgresql.auto.conf is within PGDATA, and since my
> recovery_command is there, one trick could be to touch and empty
> PGDATA/postgresql.conf, pg_rewind, remove the fake configurtion file.
> But I'm sure there is a smarter solution.
> 
> Thanks,
> Luca
> 
> 

-- 
Adrian Klaver
adrian.klaver@aklaver.com