Re: Keepalive for max_standby_delay

On Wed, 2010-05-26 at 16:22 -0700, Josh Berkus wrote:
> > Just this second posted about that, as it turns out.
> > 
> > I have a v3 *almost* ready of the keepalive patch. It still makes sense
> > to me after a few days reflection, so is worth discussion and review. In
> > or out, I want this settled within a week. Definitely need some R&R
> > here.
> 
> Does the keepalive fix all the issues with max_standby_delay?  Tom?

OK, here's v4.

Summary

* WALSender adds a timestamp onto the header of every WAL chunk sent.

* Each WAL record now has a conceptual "send timestamp" that remains
constant while that record is replayed. This is used as the basis from
which max_standby_delay is calculated when required during replay.

* Send timestamp is calculated as the later of the timestamp of chunk in
which WAL record was sent and the latest XLog time.

* WALSender sends an empty message as a keepalive when nothing else to
send. (No longer a special message type for the keepalive).

I think its close, but if there's a gaping hole here somewhere then I'll
punt for this release.

-- 
 Simon Riggs           www.2ndQuadrant.com