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If the hash functions used for hashing tuples leaked any memory, we failed to clean that up, resulting in query-lifespan memory leakage in queries using hashed subplans. One way that could happen is if the values being hashed require de-toasting, since most of our hash functions don't trouble to clean up de-toasted inputs. Prior to commit bf6c614a2, this leakage was largely masked because TupleHashTableMatch would reset hashtable->tempcxt (via execTuplesMatch). But it doesn't do that anymore, and that's not really the right place for this anyway: doing it there could reset the tempcxt many times per hash lookup, or not at all. Instead put reset calls into ExecHashSubPlan and buildSubPlanHash. Along the way to that, rearrange ExecHashSubPlan so that there's just one place to call MemoryContextReset instead of several. This amounts to accepting the de-facto API spec that the caller of the TupleHashTable routines is responsible for resetting the tempcxt adequately often. Although the other callers seem to get this right, it was not documented anywhere, so add a comment about it. Bug: #19040 Reported-by: Haiyang Li <mohen.lhy@alibaba-inc.com> Author: Haiyang Li <mohen.lhy@alibaba-inc.com> Reviewed-by: Fei Changhong <feichanghong@qq.com> Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/19040-c9b6073ef814f48c@postgresql.org Backpatch-through: 13
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/.