Latest Bitmap Index patch

Hi all,

It seems that my previous email to pgsql-hackers about the latest bitmap
index patch did not go through. Please find the latest patch in the
attachment. Any suggestions and comments are appreciated.

This patch is generated against the PostgreSQL CVS HEAD. This patch
includes: (Gavin, if I miss anything, please let me know.)

(1) Code style changes.

(2) Fixed bugs on the multi-column support, the race condition problem if
two backends try to insert the same new value (Thank Heikki for reporting
this), and some others.

(3) Added the stream bitmap implementation.

(4) Added performance improvements for creating a bitmap index.

(5) Added documentation.

There are several TODO items:

(1) Currently, the stream bitmap implementation does not support ArrayOpExpr
properly. That is, if you have a query like 'select * from T where T.a in
(1,2);' and there is a bitmap index on T.a. If the planner chooses to use
the plan using the bitmap scan, the current stream bitmap implementation
will return an incorrect result. I have been thinking about the following
two options. Either one requires quite some changes. I would like to get
some comments first before I make these changes. The options are

(a) Disable the ArrayOpExpr support while creating an execution plan for the
stream bitmap case -- use BitmapOr instead.

(b) Add a new OR logic into nodeBitmapIndexscan.c. The current OR logic
supporting hash bitmaps does not work for stream bitmaps, which handles keys
in an ArrayOpExpr one by one, which stream bitmaps require to handle keys at
the same time.

If you have any comments on this, or any suggestions on other options,
please let me know. Note: the regression test on 'create_index' will fail
because I added a check on this for the bitmap index.

(2) Add the support for range queries, such as 'where a<10'.
(3) Add a better implementation for vacuuming.

Thanks,
Jie