Simon Riggs wrote:
> The essential choice is "What would you like the max failover time to
> be?". Some users want one server with max 5 mins behind, some want two
> servers, one with 0 seconds behind, one with 12 hours behind
It's not quite that simple. Setting max_standby_delay=5mins means that
you're willing to wait 5 minutes for each query to die. Which means that
in worst case you have to stop for 5 minutes at every single vacuum
record, and fall behind much more than 5 minutes.
You could make it more like that by tracking the timestamps in commit
records, and/or having some sort of a moving average logic in the
timeout, where you allow more waiting if you haven't waited for a long
time, and kill queries more aggressively if you've had to wait a lot
recently.
It should also be noted that the control functions allow you to connect
to the database and manually pause/resume the replay. So you can for
example set max_standby_delay=0 during the day, but pause the replay
manually before starting a nightly report.
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
