rdelaage/postgresql
1
0
Fork 0
mirror of https://git.postgresql.org/git/postgresql.git synced 2024-08-20 13:33:24 +02:00
Code Issues Packages Projects Releases Wiki Activity
49,296 Commits 36 Branches 606 Tags 423 MiB
C 86%
PLpgSQL 5.5%
Perl 4.1%
Yacc 1.3%
Makefile 0.7%
Other 2.3%
044c99bc56
Go to file
Tom Lane 044c99bc56 Use query collation, not column's collation, while examining statistics. 
Commit 5e0928005 changed the planner so that, instead of blindly using
DEFAULT_COLLATION_OID when invoking operators for selectivity estimation,
it would use the collation of the column whose statistics we're
considering.  This was recognized as still being not quite the right
thing, but it seemed like a good incremental improvement.  However,
shortly thereafter we introduced nondeterministic collations, and that
creates cases where operators can fail if they're passed the wrong
collation.  We don't want planning to fail in cases where the query itself
would work, so this means that we *must* use the query's collation when
invoking operators for estimation purposes.

The only real problem this creates is in ineq_histogram_selectivity, where
the binary search might produce a garbage answer if we perform comparisons
using a different collation than the column's histogram is ordered with.
However, when the query's collation is significantly different from the
column's default collation, the estimate we previously generated would be
pretty irrelevant anyway; so it's not clear that this will result in
noticeably worse estimates in practice.  (A follow-on patch will improve
this situation in HEAD, but it seems too invasive for back-patch.)

The patch requires changing the signatures of mcv_selectivity and allied
functions, which are exported and very possibly are used by extensions.
In HEAD, I just did that, but an API/ABI break of this sort isn't
acceptable in stable branches.  Therefore, in v12 the patch introduces
"mcv_selectivity_ext" and so on, with signatures matching HEAD, and makes
the old functions into wrappers that assume DEFAULT_COLLATION_OID should
be used.  That does not match the prior behavior, but it should avoid risk
of failure in most cases.  (In practice, I think most extension datatypes
aren't collation-aware, so the change probably doesn't matter to them.)

Per report from James Lucas.  Back-patch to v12 where the problem was
introduced.

Discussion: https://postgr.es/m/CAAFmbbOvfi=wMM=3qRsPunBSLb8BFREno2oOzSBS=mzfLPKABw@mail.gmail.com
2020-06-05 16:18:50 -04:00
config Update config.guess and config.sub 2020-04-30 09:06:49 +02:00
contrib Use query collation, not column's collation, while examining statistics. 2020-06-05 16:18:50 -04:00
doc psql: Clean up terminology in \dAp command 2020-06-04 22:09:41 +02:00
src Use query collation, not column's collation, while examining statistics. 2020-06-05 16:18:50 -04:00
.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
.gitattributes gitattributes: Add new file 2019-11-12 08:13:55 +01:00
.gitignore Support for optimizing and emitting code in LLVM JIT provider. 2018-03-22 11:05:22 -07:00
aclocal.m4 Fix configure's AC_CHECK_DECLS tests to work correctly with clang. 2018-11-19 12:01:47 -05:00
configure Stamp 13beta1. 2020-05-18 16:09:19 -04:00
configure.in Stamp 13beta1. 2020-05-18 16:09:19 -04:00
COPYRIGHT Update copyrights for 2020 2020-01-01 12:21:45 -05:00
GNUmakefile.in Make install-tests target work with vpath builds 2020-05-31 18:33:00 -04:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Don't unset MAKEFLAGS in non-GNU Makefile. 2019-06-25 09:36:21 +12:00
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/.