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This function wasn't touched in commit 51004c717, but that turns out to be a bad idea, because its results now include any dead space that exists in the NOTIFY queue on account of our being lazy about advancing the queue tail. Notably, the isolation tests now fail if run twice without a server restart between, because async-notify's first test of the function will already show a positive value. It seems likely that end users would be equally unhappy about the result's instability. To fix, just make the function call asyncQueueAdvanceTail before computing its result. That should end in producing the same value as before, and it's hard to believe that there's any practical use-case where pg_notification_queue_usage() is called so often as to create a performance degradation, especially compared to what we did before. Out of paranoia, also mark this function parallel-restricted (it was volatile, but parallel-safe by default, before). Although the code seems to work fine when run in a parallel worker, that's outside the design scope of async.c, and it's a bit scary to have intentional side-effects happening in a parallel worker. There seems no plausible use-case where it'd be important to try to parallelize this, so let's not take any risk of introducing new bugs. In passing, re-pgindent async.c and run reformat-dat-files on pg_proc.dat, just because I'm a neatnik. Discussion: https://postgr.es/m/13881.1574557302@sss.pgh.pa.us
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/.