Thread: pgsql: Updated text for bitmaps: < Bitmap indexes index single
pgsql: Updated text for bitmaps: < Bitmap indexes index single
From
momjian@svr1.postgresql.org (Bruce Momjian)
Date:
Log Message: ----------- Updated text for bitmaps: < Bitmap indexes index single columns that can be combined with other bitmap < indexes to dynamically create a composite index to match a specific query. < Each index is a bitmap, and the bitmaps are bitwise AND'ed or OR'ed to be < combined. They can index by tid or can be lossy requiring a scan of the < heap page to find matching rows, or perhaps use a mixed solution where < tids are recorded for pages with only a few matches and per-page bitmaps < are used for more dense pages. Another idea is to use a 32-bit bitmap < for every page and set a bit based on the item number mod(32). > This feature allows separate indexes to be ANDed or ORed together. This > is particularly useful for data warehousing applications that need to > query the database in an many permutations. This feature scans an index > and creates an in-memory bitmap, and allows that bitmap to be combined > with other bitmap created in a similar way. The bitmap can either index > all TIDs, or be lossy, meaning it records just page numbers and each > page tuple has to be checked for validity in a separate pass. Modified Files: -------------- pgsql/doc: TODO (r1.1501 -> r1.1502) (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1501&r2=1.1502) pgsql/doc/src/FAQ: TODO.html (r1.8 -> r1.9) (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.8&r2=1.9)