index bloat in 8.4-dev

I am seeing index bloat in the current head when the indexed values are
constantly increasing, and the lower values are being constantly
deleted.

I attached a simple python script that can be fed into psql. If this is
done on 8.3.3, the number of index relpages stays fairly constant,
around 500, and doesn't change after that.

If I do this against head, then the index relpages explode, and I
stopped the test when it reached about 46k pages for about 100k live
rows.

It's possible that this has something to do with the new FSM. I checked
out a release just before the new FSM, and I did see some bloat,
reaching about 3-4k index pages for 100k live rows (which is still worse
than 8.3.3), but it did not appear to happen nearly as fast. I don't
think it's entirely the FSM though, because 8.3.3 showed no problem at
all. Perhaps the FSM just makes some problem introduced in 8.4 more
apparent?

Regards,
Jeff Davis