Re: checkpointer continuous flushing

Hi,

I just pushed the two major remaining patches in this thread. Let's see
what the buildfarm has to say; I'd not be surprised if there's some
lingering portability problem in the flushing code.

There's one remaining issue we definitely want to resolve before the
next release: Right now we always use one writeback context across all
tablespaces in a checkpoint, but Fabien's testing shows that that's
likely to hurt in a number of cases. I've some data suggesting the
contrary in others.

Things that'd be good:
* Some benchmarking. Right now controlled flushing is enabled by default
on linux, but disabled by default on other operating systems. Somebody
running benchmarks on e.g. freebsd or OSX might be good.
* If somebody has the energy to provide a windows implemenation for
flush control, that might be worthwhile. There's several places that
could benefit from that.
* The default values are basically based on benchmarking by me and Fabien.

Regards,

Andres