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Tom Lane 64e49a67e0 Repair performance regression in information_schema.triggers view. 
Commit 32ff26911 introduced use of rank() into the triggers view to
calculate the spec-mandated action_order column.  As written, this
prevents query constraints on the table-name column from being pushed
below the window aggregate step.  That's bad for performance of this
typical usage pattern, since the view now has to be evaluated for all
tables not just the one(s) the user wants to see.  It's also the cause
of some recent buildfarm failures, in which trying to evaluate the view
rows for triggers in process of being dropped resulted in "cache lookup
failed for function NNN" errors.  Those rows aren't of interest to the
test script doing the query, but the filter that would eliminate them
is being applied too late.  None of this happened before the rank()
call was there, so it's a regression compared to v10 and before.

We can improve matters by changing the rank() call so that instead of
partitioning by OIDs, it partitions by nspname and relname, casting
those to sql_identifier so that they match the respective view output
columns exactly.  The planner has enough intelligence to know that
constraints on partitioning columns are safe to push down, so this
eliminates the performance problem and the regression test failure
risk.  We could make the other partitioning columns match view outputs
as well, but it'd be more complicated and the performance benefits
are questionable.

Side note: as this stands, the planner will push down constraints on
event_object_table and trigger_schema, but not on event_object_schema,
because it checks for ressortgroupref matches not expression
equivalence.  That might be worth improving someday, but it's not
necessary to fix the immediate concern.

Back-patch to v11 where the rank() call was added.  Ordinarily we'd not
change information_schema in released branches, but the test failure has
been seen in v12 and presumably could happen in v11 as well, so we need
to do this to keep the buildfarm happy.  The change is harmless so far
as users are concerned.  Some might wish to apply it to existing
installations if performance of this type of query is of concern,
but those who don't are no worse off.

I bumped catversion in HEAD as a pro forma matter (there's no
catalog incompatibility that would really require a re-initdb).
Obviously that can't be done in the back branches.

Discussion: https://postgr.es/m/5891.1587594470@sss.pgh.pa.us
2020-04-24 12:02:36 -04:00
config Update config.guess and config.sub 2019-04-27 14:25:00 +02:00
contrib Fix cache reference leak in contrib/sepgsql. 2020-04-16 14:45:54 -04:00
doc docs: land height is "elevation", not "altitude" 2020-04-22 16:23:19 -04:00
src Repair performance regression in information_schema.triggers view. 2020-04-24 12:02:36 -04:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.gitattributes Add XSL stylesheet to fix up SVG files 2019-06-19 21:26:42 +02:00
.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 Use pkg-config, if available, to locate libxml2 during configure. 2020-03-17 12:09:26 -04:00
configure.in Use pkg-config, if available, to locate libxml2 during configure. 2020-03-17 12:09:26 -04:00
COPYRIGHT Update copyrights for 2020 2020-01-01 12:21:45 -05:00
GNUmakefile.in Integrate cpluspluscheck into build system. 2019-05-31 12:36:17 -07:00
HISTORY Change documentation references to PG website to use https: not http: 2017-05-20 21:50:47 -04:00
Makefile Don't unset MAKEFLAGS in non-GNU Makefile. 2019-06-25 09:36:21 +12:00
README Change documentation references to PG website to use https: not http: 2017-05-20 21:50:47 -04:00
README.git Change documentation references to PG website to use https: not http: 2017-05-20 21:50:47 -04:00

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/.