New features for pgbench

The attached adds two new command line switches to pgbench:

-x: Generate extended detail in the latency log, including a timestamp
for each transaction

-X: Do extra cleanup after the run (vacuum on all tables, checkpoint)
before stopping the clock. This gives substantially more consistancy in
results between runs. Most pgbench results I see people present are so
short that they're skewed considerably by whether there was a checkpoint
in the middle of the run. This also allows testing situations with
various autovacuum settings fairly.

There's an update to the README describing the features, as well as
correcting/extending some of the existing documentation.

I generated the patch from the 8.2.3 release. Since pgbench runs the same
way unless you pass it one of the new flags, I was hoping this would be
considered for the next 8.2 update. I have a series of additional scripts
I'll be releasing shortly that do interesting analysis of this extended
latency data from pgbench (graphs of TPS and latency, that sort of thing),
and I'd hate for that to only be available on 8.3.

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* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD