Commitfest patches

Bruce, you seem to have removed one of my three patches from the queue. I
would actually prefer you remove the other two and put back that one. It's the
one I most urgently need feedback on to continue.

The patch I'm so interested in receiving feedback on is the patch to preread
pages in bitmap index scans using posix_fadvise. This is basically complete
modulo documentation and autoconf tests.

However there is a larger patch struggling to get out here. The patch I
submitted just adds a new low level routine to preread blocks and doesn't
change the buffer manager routines at all. That means we have to make two
trips through the buffer manager to check if the block is present and then
subsequently to assign a buffer and read it in (from cache) synchronously.

A more invasive form of this patch would be to assign and pin a buffer when
the preread is done. That would men subsequently we would have a pinned buffer
ready to go and not need to go back to the buffer manager a second time. We
would instead just "complete" the i/o by issuing a normal read call.

The up-side would be fewer trips through the buffer manager and attendant
locking. The down-side would be stealing buffers from the shared buffers which
could be holding other pages.

I don't feel like writing the more invasive patch only to throw it out and
take the one I've already written, but I don't know what other people's
feelings are between the two. I'm leaning towards the more invasive buffer
manager changes myself.

--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
Ask me about EnterpriseDB's Slony Replication support!