Re: Streaming replication status and fail over questions

Michael Holt wrote:
> 1) I've seen things about using pg_current_xlog_location(),
> pg_last_xlog_replay_location(), pg_last_xlog_receive_location() to
> check replication status, but how can this tell me either the time lag
> or actual query lag? Do I need to wait for 9.1 and it's replication
> monitoring features?

You might want to check out repmgr:  http://projects.2ndquadrant.com/repmgr
It can collect data in the background that it uses to compute lag in
time units.

> 2) If I have a master to multi-slave setup and need to fail over, is
> there anyway for slaves to detect the new master? Without this it
> seems like fail over could be pretty messy.

repmgr also provides a view to help make this easier to figure out right
now, and the next version due out any day now will go even further
toward automating it completely.

> 3) Finally just wanted to confirm that SR allows only for replication
> of an entire server.

Well, an entire database cluster on a server.  I have put more than one
database cluster on a server before in order to make it possible to
replicate only a subset of the data.  But that's difficult to pull off,
you end up needing tools like dblink for anything that crosses the two
databases together.

--
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us
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