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As implemented in 5891c7a8ed8f, setting "force" to true in pgstat_report_wal() causes the routine to not wait for the pgstat shmem lock if it cannot be acquired, in which case the WAL and I/O statistics finish by not being flushed. The origin of the confusion comes from pgstat_flush_wal() and pgstat_flush_io(), that use "nowait" as sole argument. The I/O stats are new in v16. This is the opposite behavior of what has been used in pgstat_report_stat(), where "force" is the opposite of "nowait". In this case, when "force" is true, the routine sets "nowait" to false, which would cause the routine to wait for the pgstat shmem lock, ensuring that the stats are always flushed. When "force" is false, "nowait" is set to true, and the stats would only not be flushed if the pgstat shmem lock can be acquired, returning immediately without flushing the stats if the lock cannot be acquired. This commit changes pgstat_report_wal() so as "force" has the same behavior as in pgstat_report_stat(). There are currently three callers of pgstat_report_wal(): - Two in the checkpointer where force=true during a shutdown and the main checkpointer loop. Now the code behaves so as the stats are always flushed. - One in the main loop of the bgwriter, where force=false. Now the code behaves so as the stats would not be flushed if the pgstat shmem lock could not be acquired. Before this commit, some stats on WAL and I/O could have been lost after a shutdown, for example. Reported-by: Ryoga Yoshida Author: Ryoga Yoshida, Michael Paquier Discussion: https://postgr.es/m/f87a4d7be70530606b864fd1df91718c@oss.nttdata.com Backpatch-through: 15
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/.