On Tue, 2010-03-02 at 12:47 -0800, Marc Munro wrote: > IIUC this is only a problem for WAL from HOT updates and vacuums. If no > vacuums or HOT updates have been performed, there is no risk of > returning bad data. So WAL that does not contain HOT updates or vacuums > could be applied on the standby without risk, even if there are > long-running queries in play. This is not a complete solution but may > reduce the likelihood of queries having to be cancelled. I guess the > approach here would be to check WAL before applying it, and only cancel > queries if the WAL contains HOT updates or vacuums.
That's what we do. > Taking the idea further, if WAL records contained the tid of the latest > tuples that were overwritten, even more WAL could be applied without > having to cancel queries. > > To take it further still, if vacuum on the master could be prevented > from touching records that are less than max_standby_delay seconds old, > it would be safe to apply WAL from the very latest vacuum. I guess HOT > could be handled similarly though that may eliminate much of the > advantage of HOT updates. Thanks for your ideas. -- Simon Riggs www.2ndQuadrant.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
