On Fri, Nov 5, 2010 at 2:46 PM, Josh Berkus <j...@agliodbs.com> wrote: > I'm continuing in my efforts now to document how to deploy and manage > replication on our wiki. One of the things a DBA needs to do is to use > pg_current_xlog_location() (and related functions) to check how far > behind the master the standby is. > > However, there's some serious problems with that: > > (1) comparing these numbers is quite mathematically complex -- and, for > that matter, undocumented. > > (2) pg_rotate_xlog and/or archive_timeout will create a "gap" in the > xlog positions, quite a large one if it happens near the beginning of a > file. There is no way for any monitoring on the standby to tell the > difference between a gap created by forced rotation as opposed to being > most of a file behind, until the next record shows up. Hello, nagios > false alerts! > > (3) There is no easy way to relate a difference in log positions to an > amount of time. > > I'll work on some tools to make this a bit more palatable, but I > disagree with earlier assertions that we have the replication monitoring > "done". There's still a *lot* of work to do.
I've heard the same complaint, and I agree with your concerns. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
