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Peter Geoghegan 74388a1ac3 Avoid VACUUM reltuples distortion. 
Add a heuristic that avoids distortion in the pg_class.reltuples
estimates used by VACUUM.  Without the heuristic, successive manually
run VACUUM commands (run against a table that is never modified after
initial bulk loading) will scan the same page in each VACUUM operation.
Eventually pg_class.reltuples may reach the point where one single heap
page is accidentally considered highly representative of the entire
table.  This is likely to be completely wrong, since the last heap page
typically has fewer tuples than average for the table.

It's not obvious that this was a problem prior to commit 44fa8488, which
made vacuumlazy.c consistently scan the last heap page (even when it is
all-visible in the visibility map).  It seems possible that there were
more subtle variants of the same problem that went unnoticed for quite
some time, though.  Commit 44fa8488 simplified certain aspects of when
and how relation truncation was considered, but it did not introduce the
"scan the last page" behavior.  Essentially the same behavior was
introduced much earlier, in commit e8429082.  It was conditioned on
whether or not truncation looked promising towards the end of the
initial heap pass by VACUUM until recently, which was at least somewhat
protective.  That doesn't seem like something that we should be relying
on, though.

Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAH2-WzkNKORurux459M64mR63Aw4Jq7MBRVcX=CvALqN3A88WA@mail.gmail.com
2022-02-16 17:15:50 -08:00
config Remove configure's check for rl_completion_append_character. 2022-02-02 23:01:56 -05:00
contrib Remove all traces of tuplestore_donestoring() in the C code 2022-02-17 09:52:02 +09:00
doc Doc: Update documentation for modifying postgres_fdw foreign tables. 2022-02-16 15:15:00 +09:00
src Avoid VACUUM reltuples distortion. 2022-02-16 17:15:50 -08:00
.cirrus.yml ci: fix copy-paste mistake in 16eb8231d1. 2022-02-12 19:38:06 -08:00
.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 Add another old commit to git-blame-ignore-revs. 2021-11-03 17:34:19 -07:00
.gitattributes gitattributes: Add new entry to silence whitespace error 2021-06-05 07:57:31 +02:00
.gitignore Support for optimizing and emitting code in LLVM JIT provider. 2018-03-22 11:05:22 -07:00
aclocal.m4 Probe $PROVE not $PERL while checking for modules needed by TAP tests. 2021-11-22 12:54:52 -05:00
configure Add ./configure check for "lz4" command 2022-02-14 10:40:34 +09:00
configure.ac Add ./configure check for "lz4" command 2022-02-14 10:40:34 +09:00
COPYRIGHT Update copyright for 2022 2022-01-07 19:04:57 -05:00
GNUmakefile.in add missing tag from commit b8c4261e5e 2021-07-01 15:47:46 -04:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Dynamically find correct installation docs in Makefile. 2022-01-19 14:48:25 +01:00
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

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/.