1691512674
There's a race condition if a file changes in the source system after we have collected the file list. If the file becomes larger, we only fetched up to its original size. That can easily result in a truncated file. That's not a problem for relation files, files in pg_xact, etc. because any actions on them will be replayed from the WAL. However, configuration files are affected. This commit mitigates the race condition by fetching small files in whole, even if they have grown. A test is added in which an extra file copied is concurrently grown with the output of pg_rewind thus guaranteeing it to have changed in size during the operation. This is not a full fix: we still believe the original file size for files larger than 1 MB. That should be enough for configuration files, and doing more than that would require big changes to the chunking logic in libpq_source.c. This mitigates the race condition if the file is modified between the original scan of files and copying the file, but there's still a race condition if a file is changed while it's being copied. That's a much smaller window, though, and pg_basebackup has the same issue. This race can be seen with pg_auto_failover, which frequently uses ALTER SYSTEM, which updates postgresql.auto.conf. Often, pg_rewind will fail, because the postgresql.auto.conf file changed concurrently and a partial version of it was copied to the target. The partial file would fail to parse, preventing the server from starting up. Author: Heikki Linnakangas Reviewed-by: Cary Huang Discussion: https://postgr.es/m/f67feb24-5833-88cb-1020-19a4a2b83ac7%40iki.fi
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/.