MMAP Buffers

Hello,

If I may, I want to share some concept to use mmap in PG. It's far, far
away from perfect, but it's keeps WAL before data. As well I crated
table, with index, inserted few values, and I done vacuum full on this
table. Db inits welcome from orginal sources.

Performance of read (if backend is loaded) is really good, query time
goes down from 450ms to about 410ms. Update may be slower - but work is
in progress (I will start with write, as I went to point when simple
updates may be performed). Even that I didn't covered all aspects off
updating, it's simple to do it, just to call PreopareBufferToUpdate
before modifing buffer, ofc some ideas of increasing this are still in
my head.

Any comments, suggestions welcome.

I didn't included this, as diff, because of ~150kb size (mainly
configure scripts, which are included in SVC). Due to this, You may
download it from
http://softperience.eu/downloads/pg_mmap_20110415.diff.bz2 (Legal: Work
under PostgreSQL BSD Lincense). Patch is just GIT diff, later I will try
to grab some git.

Regards and have a nice day,
Radek.

P.S. This problem about assert with signals, I wrote... I merged with
last master, and rebuilded code. I think, I forgot to rebuild it after
previous merge.