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Diffstat (limited to 'doc/TODO')
| -rw-r--r-- | doc/TODO | 17 |
1 files changed, 8 insertions, 9 deletions
@@ -2,7 +2,7 @@ PostgreSQL TODO List ==================== Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) -Last updated: Thu Apr 21 00:09:27 EDT 2005 +Last updated: Thu Apr 21 11:20:13 EDT 2005 The most recent version of this document can be viewed at the PostgreSQL web site, http://www.PostgreSQL.org. @@ -300,14 +300,13 @@ Indexes * Allow non-bitmap indexes to be combined by creating bitmaps in memory - 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. * Allow the creation of on-disk bitmap indexes which can be quickly combined with other bitmap indexes |