> > One thing I do worry about is if both postgresql and the OS > > are both delaying write()s in the hopes of collapsing them > > at the same time. If so, this would cause both to be experience > > bigger delays than expected, and make checkpoints worse. > > That is my concern. Letting 30 seconds worth of dirty pages accumulate > between checkpoints and then trying to smooth the writes within > checkpoint code seems like a doomed effort.
30 seconds ??? You are supposed to avoid excessive checkpoints. If you are reducing checkpoint_timeout to avoid the spike, you are imho definitely tuning the wrong knob. You are supposed to increase checkpoint_timeout as far as you can to still have an acceptable recovery delay after a crash. If you cannot afford a huge spike during checkpoint, say every 30 minutes, you have to make bgwriter more aggressive. This would generally be true for both of the variants, db driven direct io and buffered filesystem io. Andreas ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
