Re: Reliability of WAL replication

On Tue, 2007-10-23 at 13:58 +0200, Marc Schablewski wrote:
> We had some corrupted data files in the past (missing clog, see
> http://archives.postgresql.org/pgsql-bugs/2007-07/msg00124.php) and are
> thinking about setting up a warm standby system using WAL replication.
>
> Would an error like the one we had appear in WAL and would it be
> replicated too? Or is there some kind of consistency check, that
> prevents broken WAL from being restored?

Each WAL record is CRC checked, so it is quite unlikely that it could be
corrupt on its own.

The contents of the WAL record may cause the system to do something
wrong on the second server, but if this occurs it usually causes some
form of error and we can see that this has happened, report the bug and
then restart replication. If that kind of error occurs it is because of
a problem in the PostgreSQL software, not a fault of the replication
technique. That means these incidents are very rare and we have quickly
fixed such bugs when they do occur. I think this has happened twice in
12-18 months.

--
Simon Riggs
2ndQuadrant http://www.2ndQuadrant.com