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Tom Lane be4b4dc759 Omit null rows when applying the Haas-Stokes estimator for ndistinct. 
Previously, we included null rows in the values of n and N that went
into the formula, which amounts to considering null as a value in its
own right; but the d and f1 values do not include nulls.  This is
inconsistent, and it contributes to significant underestimation of
ndistinct when the column is mostly nulls.  In any case stadistinct
is defined as the number of distinct non-null values, so we should
exclude nulls when doing this computation.

This is an aboriginal bug in our application of the Haas-Stokes formula,
but we'll refrain from back-patching for fear of destabilizing plan
choices in released branches.

While at it, make the code a bit more readable by omitting unnecessary
casts and intermediate variables.

Observation and original patch by Tomas Vondra, adjusted to fix both
uses of the formula by Alex Shulgin, cosmetic improvements by me
2016-04-01 15:48:24 -04:00
config Cope if platform declares mbstowcs_l(), but not locale_t, in <xlocale.h>. 2016-03-15 13:19:57 -04:00
contrib Fixes in bloom contrib module missed during review 2016-04-01 20:09:13 +03:00
doc Fix English in bloom module documentation 2016-04-01 18:47:44 +03:00
src Omit null rows when applying the Haas-Stokes estimator for ndistinct. 2016-04-01 15:48:24 -04:00
.dir-locals.el
.gitattributes Fix whitespace and remove obsolete gitattributes entry 2016-03-13 16:03:13 -04:00
.gitignore Add .gitignore entries for AIX-specific intermediate build artifacts. 2015-07-08 20:44:22 -04:00
aclocal.m4 Replace our hacked version of ax_pthread.m4 with latest upstream version. 2015-07-08 20:36:06 +03:00
configure Introduce WaitEventSet API. 2016-03-21 12:22:54 +01:00
configure.in Introduce WaitEventSet API. 2016-03-21 12:22:54 +01:00
COPYRIGHT Update copyright for 2016 2016-01-02 13:33:40 -05:00
GNUmakefile.in Fix distclean/maintainer-clean targets to remove top-level tmp_install dir. 2015-05-13 18:48:05 -04:00
HISTORY
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README
README.git

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/.