Re: Warm Standby and resetting the primary as a standby

On Wed, Aug 18, 2010 at 9:48 AM, Derrick Rice <derrick(dot)rice(at)gmail(dot)com>wrote:

> I've been reading up on the documentation for WAL shipping and warm standby
> configuration. One concern that I have (a common one, I'm sure) is that it
> seems that after bringing a standby server up as primary, other standby
> servers (including the original primary) need to be rebased before they can
> read the new primary's WALs in continuous recovery mode.
>
> It seems that the cause of this is a change to the leading digit of the WAL
> files:
>
> http://archives.postgresql.org/pgsql-general/2010-03/msg00985.php
> http://archives.postgresql.org/pgsql-admin/2009-08/msg00179.php
>
> I was hoping that someone would shed some light on this situation with a
> technical explanation. It's not clear to me why the WAL files are
> incompatible or why the digit increases. What does that first digit mean to
> postgresql? Is it possible to have the restore_command ignore the leading
> digit?
>
> I expected the WAL files to be compatible. If I start two servers from the
> same "disk image" and then they get the same exact changes recorded in WAL,
> why should the next created WAL differ depending on which server creates
> it? I imagine these two servers to have identical new versions of a "disk
> image" after consuming the exact same WALs (one generated them, the other
> read them).
>
> I'm surprised that this question doesn't come up more often or that there's
> no explanation in the docs about why its necessary to rebase a primary that
> went down gracefully (e.g. for planned maintenance)
>
> Thanks
>
> Derrick
>

Considering the high level of activity on this list, I'm surprised not to
have any discussion on this yet. Please let me know if there is a better
discussion area for this topic or if I can clarify / rephrase my question to
make it more attractive.

Barring that, I guess I'll dig into the ultimate documentation: source.

Derrick