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Building extended statistics of type "ndistinct" calls ndistinct_for_combination() once for every combination of columns. Each call allocates arrays for the whole sample and never frees them, with memory accumulating until the whole statistics object is built. The sample has 300 multiplied by target rows. With large statistics targets (default_statistics_target up to 10k), this can add up to gigabytes worth of memory, useless once a combination is computed. ndistinct_for_combination() is now called in a dedicated memory context, reset after each combination is computed. We only need the estimated number of distinct values, so there is no need to copy anything out of the memory context. Similar fixes have been done in83772cc78eandad8a166ca8for other areas of the extended stats computations. Author: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com> Discussion: https://postgr.es/m/20d6689e-f490-4ca7-a92f-e92f691ba07e@tantorlabs.com 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. 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/.