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It is relatively easy to get a replication slot to look as still active while one process is in the process of getting rid of it; when some other process tries to "acquire" the slot, it would fail with an error message of "replication slot XYZ is active for PID N". The error message in itself is fine, except that when the intention is to drop the slot, it is unhelpful: the useful behavior would be to wait until the slot is no longer acquired, so that the drop can proceed. To implement this, we use a condition variable so that slot acquisition can be told to wait on that condition variable if the slot is already acquired, and we make any change in active_pid broadcast a signal on the condition variable. Thus, as soon as the slot is released, the drop will proceed properly. Reported by: Tom Lane Discussion: https://postgr.es/m/11904.1499039688@sss.pgh.pa.us Authors: Petr Jelínek, Álvaro Herrera
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/.