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In replication, when we shutdown the master, walsender tries to send all the outstanding WAL records to the standby, and then to exit. This basically means that all the WAL records are fully synced between two servers after the clean shutdown of the master. So, after promoting the standby to new master, we can restart the stopped master as new standby without the need for a fresh backup from new master. But there was one problem so far: though walsender tries to send all the outstanding WAL records, it doesn't wait for them to be replicated to the standby. Then, before receiving all the WAL records, walreceiver can detect the closure of connection and exit. We cannot guarantee that there is no missing WAL in the standby after clean shutdown of the master. In this case, backup from new master is required when restarting the stopped master as new standby. This patch fixes this problem. It just changes walsender so that it waits for all the outstanding WAL records to be replicated to the standby before closing the replication connection. Per discussion, this is a fix that needs to get backpatched rather than new feature. So, back-patch to 9.1 where enough infrastructure for this exists. Patch by me, reviewed by Andres Freund.
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. Changes between all PostgreSQL releases are recorded in the file HISTORY. 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/.