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The 028_pitr_timelines.pl test would sometimes hang, waiting for a WAL segment that was just filled up to be archived. It was because the test used 'pg_stat_archiver.last_archived_wal' to check if a file was archived, but the order that WAL files are archived when a standby is promoted is not fully deterministic, and 'last_archived_wal' tracks the last segment that was archived, not the highest-numbered WAL segment. Because of that, if the archiver archived segment 3, and then 2, 'last_archived_wal' say 2, and the test query would think that 3 has not been archived yet. Normally, WAL files are marked ready for archival in order, and the archiver process will process them in order, so that issue doesn't arise. We have used the same query on 'last_archived_wal' in a few other tests with no problem. But when a standby is promoted, things are a bit chaotic. After promotion, the server will try to archive all the WAL segments from the old timeline that are in pg_wal, as well as the history file and any new WAL segments on the new timeline. The end-of-recovery checkpoint will create the .ready files for all the WAL files on the old timeline, but at the same time, the new timeline is opened up for business. A file from the new timeline can therefore be archived before the files from the old timeline have been marked as ready for archival. It turns out that we don't really need to wait for the archival in this particular test, because the standby server is about to be stopped, and stopping a server will wait for the end-of-recovery checkpoint and all WAL archivals to finish, anyway. So we can just remove it from the test. Add a note to the docs on 'pg_stat_archiver' view that files can be archived out of order. Reviewed-by: Tom Lane Discussion: https://www.postgresql.org/message-id/3186114.1644960507@sss.pgh.pa.us |
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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/.