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Tom Lane 8a906204ae Fix race condition during replication origin drop. 
replorigin_drop() misunderstood the API for condition variables: it
had ConditionVariablePrepareToSleep and ConditionVariableCancelSleep
inside its test-and-sleep loop, rather than outside the loop as
intended.  The net effect is a narrow race-condition window wherein,
if the process using a replication slot releases it immediately after
replorigin_drop() releases the ReplicationOriginLock, replorigin_drop()
would get into the condition variable's wait list too late and then
wait indefinitely for a signal that won't come.

Because there's a different CV for each replication slot, we can't
just move the ConditionVariablePrepareToSleep call to above the
test-and-sleep loop.  What we can do, in the wake of commit 13db3b936,
is drop the ConditionVariablePrepareToSleep call entirely.  This fix
depends on that commit because (at least in principle) the slot matching
the target replication origin might move around, so that once in a blue
moon successive loop iterations might involve different CVs.  We can now
cope with such a scenario, at the cost of an extra trip through the
retry loop.

(There are ways we could fix this bug without depending on that commit,
but they're all a lot more complicated than this way.)

While at it, upgrade the rather skimpy comments in this function.

Back-patch to v10 where this code came in.

Discussion: https://postgr.es/m/19947.1515455433@sss.pgh.pa.us
2018-01-09 12:09:30 -05:00
config Try harder to detect unavailability of __builtin_mul_overflow(int64). 2017-12-17 11:52:22 -05:00
contrib Fix new test case to not be endian-dependent. 2018-01-04 16:00:21 -05:00
doc Improve scripting language in pgbench 2018-01-09 18:02:04 +03:00
src Fix race condition during replication origin drop. 2018-01-09 12:09:30 -05:00
.dir-locals.el
.gitattributes Remove contrib/tsearch2. 2017-02-13 11:06:11 -05:00
.gitignore Add lcov --initial 2017-09-29 08:54:34 -04:00
aclocal.m4 Make configure check for IPC::Run when --enable-tap-tests is specified. 2017-06-15 15:56:12 -04:00
configure Another attempt at fixing build with various OpenSSL versions 2018-01-04 19:09:27 -05:00
configure.in Another attempt at fixing build with various OpenSSL versions 2018-01-04 19:09:27 -05:00
COPYRIGHT Update copyright for 2018 2018-01-02 23:30:12 -05:00
GNUmakefile.in Have "make coverage" recurse into contrib as well 2016-09-05 18:44:36 -03:00
HISTORY Change documentation references to PG website to use https: not http: 2017-05-20 21:50:47 -04:00
Makefile Fix non-GNU makefiles for AIX make. 2017-11-30 00:57:22 -08:00
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/.