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< 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. |
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PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. The JDBC, ODBC, C++, Python, and Tcl interfaces have been moved to the PostgreSQL Projects Web Site at http://gborg.postgresql.org for separate maintenance. A Perl DBI/DBD driver is available from CPAN. See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Changes between all PostgreSQL releases are recorded in the file HISTORY. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at ftp://ftp.postgresql.org/pub/. For more information look at our web site located at http://www.postgresql.org/.