On Fri, 1 Jun 2007, Ron Johnson wrote:
How difficult would it be to modify the process (the postmaster?) that writes
the xlogs(?) to tee them to a listening process across the cloud on the DR
machine, which then applies them to the DR database?
On an 8.2 server, you can practically do this right now by aggressively
using the pg_xlogfile_name_offset() function and piping the data over to
somewhere else. See section 23.4.4 of
http://www.postgresql.org/docs/8.2/static/warm-standby.html
It's not quite putting a "tee" in the engine itself, but there's not a lot
of practial difference if you're copying over the data only a moment after
it appears with the offset function instead; it's just a different set of
efficiency trade-offs (more polling the way it's implemented, but the base
engine never gets held up waiting for network I/O to the DR box).
P.S. it's not the "the cloud" anymore, it's "the tubes".
This then begs the question: are CREATE|ALTER TABLESPACE commands stored in
the xlogs?
See section 23.3.5 of
http://www.postgresql.org/docs/8.2/static/continuous-archiving.html for
information about what goes into the WAL when you do that. You'd need to
implement a process that made sure to sync changes in the underlying
filesystem before modifying a tablespace.
--
* Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD
