pgsql: Updated text for bitmaps: < Bitmap indexes index single
Log Message:
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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:
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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)