81f7738953
Accidentally the code in LWLockWakeup() checked the list of to-be-woken up processes to see if LW_FLAG_HAS_WAITERS should be unset. That means that HAS_WAITERS would not get unset immediately, but only during the next, unnecessary, call to LWLockWakeup(). Luckily, as the code stands, this is just a small efficiency issue. However, if there were (as in a patch of mine) a case in which LWLockWakeup() would not find any backend to wake, despite the wait list not being empty, we'd wrongly unset LW_FLAG_HAS_WAITERS, leading to potentially hanging. While the consequences in the backbranches are limited, the code as-is confusing, and it is possible that there are workloads where the additional wait list lock acquisitions hurt, therefore backpatch. Discussion: https://postgr.es/m/fvfmkr5kk4nyex56ejgxj3uzi63isfxovp2biecb4bspbjrze7@az2pljabhnff Backpatch-through: 14
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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.