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Tom Lane bd371ea5c0 Fix logical errors in tsquery selectivity estimation for prefix queries. 
I made multiple errors in commit 97532f7c29,
stemming mostly from failure to think about the available frequency data
as being element frequencies not value frequencies (so that occurrences of
different elements are not mutually exclusive).  This led to sillinesses
such as estimating that "word" would match more rows than "word:*".

The choice to clamp to a minimum estimate of DEFAULT_TS_MATCH_SEL also
seems pretty ill-considered in hindsight, as it would frequently result in
an estimate much larger than the available data suggests.  We do need some
sort of clamp, since a pattern not matching any of the MCELEMs probably
still needs a selectivity estimate of more than zero.  I chose instead to
clamp to at least what a non-MCELEM word would be estimated as, preserving
the property that "word:*" doesn't get an estimate less than plain "word",
whether or not the word appears in MCELEM.

Per investigation of a gripe from Bill Martin, though I suspect that his
example case actually isn't even reaching the erroneous code.

Back-patch to 9.1 where this code was introduced.
2012-09-11 21:23:49 -04:00
config Don't reject threaded Python on FreeBSD. 2012-02-20 16:21:35 -05:00
contrib Fix line end mishandling in pg_upgrade on Windows. 2012-09-05 17:49:09 -04:00
doc Document how to prevent PostgreSQL itself from exhausting memory. 2012-08-30 14:23:05 -04:00
src Fix logical errors in tsquery selectivity estimation for prefix queries. 2012-09-11 21:23:49 -04:00
.gitignore Add gitignore for mingw/cygwin build outputs 2011-06-09 18:11:47 +02:00
aclocal.m4 Remove cvs keywords from all files. 2010-09-20 22:08:53 +02:00
configure Make configure probe for mbstowcs_l as well as wcstombs_l. 2012-08-31 14:18:08 -04:00
configure.in Make configure probe for mbstowcs_l as well as wcstombs_l. 2012-08-31 14:18:08 -04:00
COPYRIGHT Stamp copyrights for year 2011. 2011-01-01 13:18:15 -05:00
GNUmakefile.in Build src/ before contrib/ in make world 2011-08-24 21:36:53 +03:00
Makefile Allow make check in PL directories 2011-02-15 06:52:12 +02:00
README Remove useless whitespace at end of lines 2010-11-23 22:34:55 +02:00
README.git Trivial typo fix. 2010-09-21 14:16:00 -04:00

README 

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.

PostgreSQL has many language interfaces, many of which are listed here:

	http://www.postgresql.org/download

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
http://www.postgresql.org/download/.  For more information look at our
web site located at http://www.postgresql.org/.