Re: Patch to add a feature to pg_standby

[Simon Riggs <simon(at)2ndquadrant(dot)com>]

On Wed, 2008-04-30 at 11:29 +0100, Heikki Linnakangas wrote:
> chris(dot)johnson(at)desknetinc(dot)com wrote:
> > When using pg_standby to remain in recovery mode on a warm standby system,
> > if there is a need to perform other actions in coordination with recovery
> > actions, the -x <auxiliary command> option implemented by this patch
> > enables that coordination.  I considered adding the ability to override the
> > restoreCommand, however by keeping this separate and optional it is
> > possible to force retries of the auxiliary command until successful and
> > still utilize pg_usleep instead of looping within an external script or
> > command.  And the previous behavior of pg_standby remains unchanged (other
> > than debug logging and documenting the option in usage) if the new option
> > is omitted.
> > 
> > I added this feature to help with synchronization of a content repository
> > consisting of a PostgreSQL db for meta-information and a separate file
> > store for content.
> > The auxiliary command enables forcing an rsync of the file store that is at
> > least as current as the found WAL segment file's db changes, and prevents
> > recovery of that WAL file unless the rsync can be performed successfully.
> > 
> > (See attached file: pg_standby.c.diff)
> 
> This could be implemented by a "pass-through" restore_command, that 
> calls pg_standby, and does the custom action when pg_standby returns 
> successfully. 

Yes, that's the preferred route for most cases.

pg_standby was designed to be customisable, so if it works for Chris,
thats OK.

After some mulling on this, I'm not sure we need to include this in
pg_standby however. If we did we'd end up having before/after commands
and retry options etc.

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