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This assertion, based on pending_since (timestamp used to prevent stats reports to be too frequent or should a partial flush happen), is reached when it is found that no data can be flushed but a previous call of pgstat_report_stat() determined that some stats data has been found as in need of a flush. So pending_since is set when some stats data is pending (in non-force mode) or if report attempts are too frequent, and reset to 0 once all stats have been flushed. Since 5cbbe70a9cc6, WAL senders have begun to report their stats on a periodic basis for IO stats in v16~ and backend stats on HEAD, creating some friction with the concurrent pgstat_report_stat() calls that can happen in the context of a WAL sender (shutdown callback doing a final report or backend-related code paths). This problem is the cause of spurious failures in the TAP tests. In theory, this assertion can be also reached in v15, even if that's very unlikely. For example, a process, say a background worker, could do periodic and direct stats flushes with concurrent calls of pgstat_report_stat() that could cause conflicting values of pending_since. This can be done with WAL or SLRU stats flushes using pgstat_flush_wal() or pgstat_slru_flush(). HEAD makes this situation easier to happen with custom cumulative stats. This commit removes the assertion altogether, per discussion, as it is more useful to keep the state of things as they are for the WAL sender. The assertion could use a special state based on for example am_walsender, but I doubt that this would be meaningful in the long run based on the other arguments raised while discussing this issue. Reported-by: Tom Lane <tgl@sss.pgh.pa.us> Reported-by: Andres Freund <andres@anarazel.de> Discussion: https://postgr.es/m/1489124.1744685908@sss.pgh.pa.us Discussion: https://postgr.es/m/dwrkeszz6czvtkxzr5mqlciy652zau5qqnm3cp5f3p2po74ppk@omg4g3cc6dgq 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/.