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Up to now, async.c scanned its whole array of per-backend state whenever it needed to find listening backends. That's expensive if MaxBackends is large, so extend the data structure with list links that thread the active entries together. A downside of this change is that asyncQueueUnregister (unregister a listening backend at backend exit) now requires exclusive not shared lock, and it can take awhile if there are many other listening backends. We could improve the latter issue by using a doubly- not singly-linked list, but it's probably not worth the storage space; typical usage patterns for LISTEN/NOTIFY have fairly long-lived listeners. In return for that, Exec_ListenPreCommit (initially register a listening backend), SignalBackends, and asyncQueueAdvanceTail get significantly faster when MaxBackends is much larger than the number of listening backends. If most of the potential backend slots are listening, we don't win, but that's a case where the actual interprocess-signal overhead is going to swamp these considerations anyway. Martijn van Oosterhout, hacked a bit more by me Discussion: https://postgr.es/m/CADWG95vtRBFDdrx1JdT1_9nhOFw48KaeTev6F_LtDQAFVpSPhA@mail.gmail.com
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/.