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Tom Lane a102f98e26 Mark read/write expanded values as read-only in ExecProject(). 
If a plan node output expression returns an "expanded" datum, and that
output column is referenced in more than one place in upper-level plan
nodes, we need to ensure that what is returned is a read-only reference
not a read/write reference.  Otherwise one of the referencing sites could
scribble on or even delete the expanded datum before we have evaluated the
others.  Commit 1dc5ebc907, which introduced this feature, supposed
that it'd be sufficient to make SubqueryScan nodes force their output
columns to read-only state.  The folly of that was revealed by bug #14174
from Andrew Gierth, and really should have been immediately obvious
considering that the planner will happily optimize SubqueryScan nodes
out of the plan without any regard for this issue.

The safest fix seems to be to make ExecProject() force its results into
read-only state; that will cover every case where a plan node returns
expression results.  Actually we can delegate this to ExecTargetList()
since we can recursively assume that plain Vars will not reference
read-write datums.  That should keep the extra overhead down to something
minimal.  We no longer need ExecMakeSlotContentsReadOnly(), which was
introduced only in support of the idea that just a few plan node types
would need to do this.

In the future it would be nice to have the planner account for this problem
and inject force-to-read-only expression evaluation nodes into only the
places where there's a risk of multiple evaluation.  That's not a suitable
solution for 9.5 or even 9.6 at this point, though.

Report: <20160603124628.9932.41279@wrigleys.postgresql.org>
2016-06-03 15:14:35 -04:00
config Fix configure's incorrect version tests for flex and perl. 2016-05-02 11:18:10 -04:00
contrib Ensure plan stability in contrib/btree_gist regression test. 2016-05-12 20:04:39 -04:00
doc Fix typo in CREATE DATABASE syntax synopsis. 2016-05-31 12:05:30 -04:00
src Mark read/write expanded values as read-only in ExecProject(). 2016-06-03 15:14:35 -04:00
.dir-locals.el emacs: Set indent-tabs-mode in perl-mode 2015-04-12 23:53:23 -04:00
.gitattributes Add functions for dealing with PGP armor header lines to pgcrypto. 2014-10-01 16:03:39 +03:00
.gitignore Improve speed of make check-world 2015-04-23 08:59:52 -04:00
aclocal.m4 Revert changes to pthread configure tests on REL9_5_STABLE. 2015-07-09 10:59:10 +03:00
configure Stamp 9.5.3. 2016-05-09 16:50:23 -04:00
configure.in Stamp 9.5.3. 2016-05-09 16:50:23 -04:00
COPYRIGHT Update copyright for 2016 2016-01-02 13:33:39 -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 Improve text of stub HISTORY file. 2014-02-12 18:16:17 -05:00
Makefile Allow make check in PL directories 2011-02-15 06:52:12 +02:00
README Don't generate plain-text HISTORY and src/test/regress/README anymore. 2014-02-10 20:48:04 -05:00
README.git Don't generate plain-text HISTORY and src/test/regress/README anymore. 2014-02-10 20:48:04 -05:00

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:

	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/.