On Fri, 2008-09-12 at 09:45 +0100, Simon Riggs wrote: > On Thu, 2008-09-11 at 15:42 +0300, Heikki Linnakangas wrote: > > Gregory Stark wrote: > > > b) vacuum on the server which cleans up a tuple the slave has in scope > > > has to > > > block WAL reply on the slave (which I suppose defeats the purpose of > > > having > > > a live standby for users concerned more with fail-over latency). > > > > One problem with this, BTW, is that if there's a continuous stream of > > medium-length transaction in the slave, each new snapshot taken will > > prevent progress in the WAL replay, so the WAL replay will advance in > > "baby steps", and can fall behind indefinitely. As soon as there's a > > moment that there's no active snapshot, it can catch up, but if the > > slave is seriously busy, that might never happen. > > It should be possible to do mixed mode. > > Stall WAL apply for up to X seconds, then cancel queries. Some people > may want X=0 or low, others might find X = very high acceptable (Merlin > et al).
Or even milder version. * Stall WAL apply for up to X seconds, * then stall new queries, let old ones run to completion (with optional fallback to canceling after Y sec), * apply WAL. * Repeat. ------------- Hannu -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
