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Programmers discovered decades ago that it was useful to have a simple interface for allocating and freeing memory, which is why malloc() and free() were invented. Unfortunately, those handy tools don't work with dynamic shared memory segments because those are specific to PostgreSQL and are not necessarily mapped at the same address in every cooperating process. So invent our own allocator instead. This makes it possible for processes cooperating as part of parallel query execution to allocate and free chunks of memory without having to reserve them prior to the start of execution. It could also be used for longer lived objects; for example, we could consider storing data for pg_stat_statements or the stats collector in shared memory using these interfaces, rather than writing them to files. Basically, anything that needs shared memory but can't predict in advance how much it's going to need might find this useful. Thomas Munro and Robert Haas. The original code (of mine) on which Thomas based his work was actually designed to be a new backend-local memory allocator for PostgreSQL, but that hasn't gone anywhere - or not yet, anyway. Thomas took that work and performed major refactoring and extensive modifications to make it work with dynamic shared memory, including the addition of appropriate locking. Discussion: CA+TgmobkeWptGwiNa+SGFWsTLzTzD-CeLz0KcE-y6LFgoUus4A@mail.gmail.com Discussion: CAEepm=1z5WLuNoJ80PaCvz6EtG9dN0j-KuHcHtU6QEfcPP5-qA@mail.gmail.com |
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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: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.