37450f2ca9
This fixes a bug in simplehash.h which caused an incorrect size mask to be used when the hash table grew to SH_MAX_SIZE (2^32). The code was incorrectly setting the size mask to 0 when the hash tables reached the maximum possible number of buckets. This would result always trying to use the 0th bucket causing an infinite loop of trying to grow the hash table due to there being too many collisions. Seemingly it's not that common for simplehash tables to ever grow this big as this bug dates back to v10 and nobody seems to have noticed it before. However, probably the most likely place that people would notice it would be doing a large in-memory Hash Aggregate with something close to at least 2^31 groups. After this fix, the code now works correctly with up to within 98% of 2^32 groups and will fail with the following error when trying to insert any more items into the hash table: ERROR: hash table size exceeded However, the work_mem (or hash_mem_multiplier in newer versions) settings will generally cause Hash Aggregates to spill to disk long before reaching that many groups. The minimal test case I did took a work_mem setting of over 192GB to hit the bug. simplehash hash tables are used in a few other places such as Bitmap Index Scans, however, again the size that the hash table can become there is also limited to work_mem and it would take a relation of around 16TB (2^31) pages and a very large work_mem setting to hit this. With smaller work_mem values the table would become lossy and never grow large enough to hit the problem. Author: Yura Sokolov Reviewed-by: David Rowley, Ranier Vilela Discussion: https://postgr.es/m/b1f7f32737c3438136f64b26f4852b96@postgrespro.ru Backpatch-through: 10, where simplehash.h was added
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/.