Re: Final background writer cleanup for 8.3

"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> Any tests which focus just on throughput don't address the problems which
> caused us so much grief.

This is a good point: a steady-state load is either going to be in the
regime where you're not write-bottlenecked, or the one where you are;
and either way the bgwriter isn't going to look like it helps much.

The real use of the bgwriter, perhaps, is to smooth out a varying load
so that you don't get pushed into the write-bottlenecked mode during
spikes. We've already had to rethink the details of how we made that
happen with respect to preventing checkpoints from causing I/O spikes.
Maybe LRU buffer flushes need a rethink too.

Right at the moment I'm still comfortable with what Greg is doing, but
there's an argument here for a more aggressive scaling factor on
number-of-buffers-to-write than he thinks. Still, as long as we have a
GUC variable in there, tuning should be possible.

regards, tom lane