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When the checkpointer writes the shutdown checkpoint, it checks afterwards whether any WAL has been written since it started and throws a PANIC if so. At that point, only walsenders are still active, so one might think this could not happen, but walsenders can also generate WAL, for instance in BASE_BACKUP and certain variants of CREATE_REPLICATION_SLOT. So they can trigger this panic if such a command is run while the shutdown checkpoint is being written. To fix this, divide the walsender shutdown into two phases. First, the postmaster sends a SIGUSR2 signal to all walsenders. The walsenders then put themselves into the "stopping" state. In this state, they reject any new commands. (For simplicity, we reject all new commands, so that in the future we do not have to track meticulously which commands might generate WAL.) The checkpointer waits for all walsenders to reach this state before proceeding with the shutdown checkpoint. After the shutdown checkpoint is done, the postmaster sends SIGINT (previously unused) to the walsenders. This triggers the existing shutdown behavior of sending out the shutdown checkpoint record and then terminating. Author: Michael Paquier <michael.paquier@gmail.com> Reported-by: Fujii Masao <masao.fujii@gmail.com>
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/.