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Peter Geoghegan 3097bde7dd Avoid reltuples distortion in very small tables. 
Consistently avoid trusting a sample of only one page at the point that
VACUUM determines a new reltuples for the target table (though only when
the table is larger than a single page).  This is follow-up work to
commit 74388a1a, which added a heuristic to prevent reltuples from
becoming distorted by successive VACUUM operations that each scan only a
single heap page (which was itself more or less a bugfix for an issue in
commit 44fa8488, which simplified VACUUM's handling of scanned pages).

The original bugfix commit did not account for certain remaining cases
that where not affected by its "2% of total relpages" heuristic.  This
happened with relations that are small enough that just one of its pages
exceeded the 2% threshold, yet still big enough for VACUUM to deem
skipping most of its pages via the visibility map worthwhile.  reltuples
could still become distorted over time with such a table, at least in
scenarios where the VACUUM command is run repeatedly and without the
table itself ever changing.

Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAH2-Wzk7d4m3oEbEWkWQKd+gz-eD_peBvdXVk1a_KBygXadFeg@mail.gmail.com
Backpatch: 15-, where the rules for scanned pages changed.
 		2022-08-19 09:26:08 -07:00
config Remove replacement code for getaddrinfo. 2022-08-14 09:53:28 +12:00
contrib Use correct LSN for error reporting in pg_walinspect 2022-08-18 14:23:30 -07:00
doc doc: Improve some markups and some wording around archiving modules 2022-08-19 10:00:12 +09:00
src Avoid reltuples distortion in very small tables. 2022-08-19 09:26:08 -07:00
.cirrus.yml ci: remove minor version from freebsd image name 2022-07-31 18:51:47 -07:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Add .editorconfig 2019-12-18 09:13:13 +01:00
.git-blame-ignore-revs Backpatch addition of .git-blame-ignore-revs 2022-08-05 19:36:24 +02:00
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GNUmakefile.in Run tests of libpq on installcheck-world, checkprep and check-world 2022-06-03 13:15:20 +09:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
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README Canonicalize some URLs 2020-02-10 20:47:50 +01:00
README.git Canonicalize some URLs 2020-02-10 20:47:50 +01:00
aclocal.m4 Probe $PROVE not $PERL while checking for modules needed by TAP tests. 2021-11-22 12:54:52 -05:00
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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:

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