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The Memoize executor node stores the cache key values along with the tuple(s) which were found in the outer node which match each key value, however, when the planner tried to estimate how many entries could be stored in the cache, it didn't take into account that the cache key must also be stored. In many cases, this won't make a large difference as the key is likely small in comparison to the tuple(s) being stored, however, it's not impossible to craft cases where the key could take more memory than the tuple(s) stored for it. Here we adjust the planner so it takes into account the estimated amount of memory to store the cache key. Effectively, this change will reduce the estimated cache hit ratio when it's thought that not all items will fit in the cache, thus Memoize will become more expensive in such cases. The executor already takes into account the memory consumed by the cache key, so here we only need to adjust the planner. Discussion: https://postgr.es/m/CAApHDvqGErGuyBfQvBQrTCHDbzLTqoiW=_G9sOzeFxWEc_7auA@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/.