b81d08d600
This fixes an oversight from c6c3334 which has introduced a more strict ordering in the way WAL senders are stopped to prevent current WAL activity when a shutdown checkpoint is created. After all backends are stopped, all WAL senders are requested to stop which makes them stop any activity, and switching their state as stopping. Once the checkpointer knows that all WAL senders are in a stopping state, the shutdown checkpoint can begin, with all WAL senders activated, waiting for their clients to flush the shutdown checkpoint record. If a subset of WAL senders are stopping and in a sync state, other WAL senders could still be waiting for a WAL position to be synced while committing a transaction, however the subset of stopping senders would not release waiters, potentially breaking synchronous replication guarantees. This commit makes sure that even WAL senders stopping are able to release waiters properly. On 9.4, this can also trigger an assertion failure when setting for example max_wal_senders to 1 where a WAL sender is not able to find itself as in synchronous state when the instance stops. Reported-by: Paul Guo Author: Paul Guo, Michael Paquier Discussion: https://postgr.es/m/CAEET0ZEv8VFqT3C-cQm6byOB4r4VYWcef1J21dOX-gcVhCSpmA@mail.gmail.com Backpatch-through: 9.4
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/.