On 5 December 2012 16:40, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> The real question here probably needs to be "what is the point of
> recoveryPauseAtTarget in the first place?". I find it hard to envision
> what's the point of pausing unless the user has an opportunity to
> make a decision about whether to continue applying WAL. As Simon
> mentioned, we seem to be lacking some infrastructure that would let
> the user adjust the recovery_target parameters before resuming WAL
> processing. But, assuming for the moment that our workaround for
> that is "shutdown the server, adjust recovery.conf, and restart",
> is the pause placed in a useful spot for that?
> BTW, could we make this more convenient by letting recoveryPausesHere()
> reread recovery.conf? Also, shouldn't the code re-evaluate
> recoveryStopsHere() after that?
The recovery target and the consistency point are in some ways in
conflict. If the recovery target is before the consistency point there
is no point in stopping there, whether or not we pause. What we should
do is say "recovery target reached, yet recovery not yet consistent,
continuing".
So ISTM that we should make recoveryStopsHere() return false while we
are inconsistent. Problems solved.
We can re-read parameters after we wake from a pause. Presumably only
in HEAD, or do you mean in 9.2/9,1 also?
My earlier patch to rearrange pause logic did a few things, nothing
very dramatic
* Put the logic for whether we're consistent inside
recoveryPausesHere() as requested
* rearrange logic so setting EndPtr is the very last thing we do
before redo for the current record
* Fixes the bug that we don't pause in the correct place if recoveryApply = true
The comment on that new pause location was slightly wrong
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
