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Robert Haas ae9bfc5d65 postgres_fdw: Allow cancellation of transaction control commands. 
Commit f039eaac71, later back-patched
with commit 1b812afb0e, allowed many of
the queries issued by postgres_fdw to fetch remote data to respond to
cancel interrupts in a timely fashion.  However, it didn't do anything
about the transaction control commands, which remained
noninterruptible.

Improve the situation by changing do_sql_command() to retrieve query
results using pgfdw_get_result(), which uses the asynchronous
interface to libpq so that it can check for interrupts every time
libpq returns control.  Since this might result in a situation
where we can no longer be sure that the remote transaction state
matches the local transaction state, add a facility to force all
levels of the local transaction to abort if we've lost track of
the remote state; without this, an apparently-successful commit of
the local transaction might fail to commit changes made on the
remote side.  Also, add a 60-second timeout for queries issue during
transaction abort; if that expires, give up and mark the state of
the connection as unknown.  Drop all such connections when we exit
the local transaction.  Together, these changes mean that if we're
aborting the local toplevel transaction anyway, we can just drop the
remote connection in lieu of waiting (possibly for a very long time)
for it to complete an abort.

This still leaves quite a bit of room for improvement.  PQcancel()
has no asynchronous interface, so if we get stuck sending the cancel
request we'll still hang.  Also, PQsetnonblocking() is not used, which
means we could block uninterruptibly when sending a query.  There
might be some other optimizations possible as well.  Nonetheless,
this allows us to escape a wait for an unresponsive remote server
quickly in many more cases than previously.

Report by Suraj Kharage.  Patch by me and Rafia Sabih.  Review
and testing by Amit Kapila and Tushar Ahuja.

Discussion: http://postgr.es/m/CAF1DzPU8Kx+fMXEbFoP289xtm3bz3t+ZfxhmKavr98Bh-C0TqQ@mail.gmail.com
 		2017-06-07 15:14:55 -04:00
config Update config.guess and config.sub 2017-05-14 11:09:34 -04:00
contrib postgres_fdw: Allow cancellation of transaction control commands. 2017-06-07 15:14:55 -04:00
doc Fix some cases of "the the" split across two lines. 2017-06-06 12:24:44 -04:00
src Fix updating of pg_subscription_rel from workers 2017-06-07 13:49:14 -04:00
.dir-locals.el emacs: Set indent-tabs-mode in perl-mode 2015-04-12 23:53:23 -04:00
.gitattributes Remove contrib/tsearch2. 2017-02-13 11:06:11 -05:00
.gitignore Allow .so minor version numbers above 9 in .gitignore. 2016-08-15 17:35:35 -04:00
COPYRIGHT Update copyright for 2017 2017-01-03 12:37:53 -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 Allow make check in PL directories 2011-02-15 06:52:12 +02:00
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
aclocal.m4 ICU support 2017-03-23 15:28:48 -04:00
configure Stamp 10beta1. 2017-05-15 17:20:59 -04:00
configure.in Stamp 10beta1. 2017-05-15 17:20:59 -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/.