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Robert Haas 4ea51cdfe8 Use abbreviated keys for faster sorting of text datums. 
This commit extends the SortSupport infrastructure to allow operator
classes the option to provide abbreviated representations of Datums;
in the case of text, we abbreviate by taking the first few characters
of the strxfrm() blob.  If the abbreviated comparison is insufficent
to resolve the comparison, we fall back on the normal comparator.
This can be much faster than the old way of doing sorting if the
first few bytes of the string are usually sufficient to resolve the
comparison.

There is the potential for a performance regression if all of the
strings to be sorted are identical for the first 8+ characters and
differ only in later positions; therefore, the SortSupport machinery
now provides an infrastructure to abort the use of abbreviation if
it appears that abbreviation is producing comparatively few distinct
keys.  HyperLogLog, a streaming cardinality estimator, is included in
this commit and used to make that determination for text.

Peter Geoghegan, reviewed by me.
2015-01-19 15:28:27 -05:00
config Remove configure test for nonstandard variants of getpwuid_r(). 2015-01-11 12:52:37 -05:00
contrib Rearrange explain.c's API so callers need not embed sizeof(ExplainState). 2015-01-15 13:39:33 -05:00
doc doc: Fix typos in make_timestamp{,tz} examples 2015-01-19 12:43:58 -03:00
src Use abbreviated keys for faster sorting of text datums. 2015-01-19 15:28:27 -05:00
.dir-locals.el Update Emacs configuration 2013-08-13 20:08:44 -04:00
.gitattributes Add functions for dealing with PGP armor header lines to pgcrypto. 2014-10-01 16:03:39 +03:00
.gitignore Update .gitignore for config.cache. 2014-12-18 19:56:42 +09:00
aclocal.m4 Remove cvs keywords from all files. 2010-09-20 22:08:53 +02:00
configure Allow CFLAGS from configure's environment to override automatic CFLAGS. 2015-01-14 11:08:13 -05:00
configure.in Allow CFLAGS from configure's environment to override automatic CFLAGS. 2015-01-14 11:08:13 -05:00
COPYRIGHT Update copyright for 2015 2015-01-06 11:43:47 -05:00
GNUmakefile.in Add TAP tests for client programs 2014-04-14 21:33:46 -04:00
HISTORY Improve text of stub HISTORY file. 2014-02-12 18:16:17 -05:00
Makefile Allow make check in PL directories 2011-02-15 06:52:12 +02:00
README Don't generate plain-text HISTORY and src/test/regress/README anymore. 2014-02-10 20:48:04 -05:00
README.git Don't generate plain-text HISTORY and src/test/regress/README anymore. 2014-02-10 20:48:04 -05:00

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.  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/.