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adf97c156allowed expression evaluation to perform hashing, and subsequently9ca67658dfixed a memory stomping bug in that commit that caused unrelated-to-hashing expression op steps to stomp on the intermediate hash value. The intermediate hash value needs to be maintained when hashing multiple hash keys.9ca67658ddidn't quite get things right when in "strict" mode when it aborted hashing early after encountering a NULL hash key. What was meant to happen was that the expression returns NULL directly to indicate to the caller the value hashed to NULL. The problem was that any EEOP_HASHDATUM_FIRST_STRICT or EEOP_HASHDATUM_NEXT32_STRICT op step that didn't belong to the final key to be hashed would have its op->resnull and op->resvalue pointing to the location to store the intermediate hash value. That's correct for non-NULLs since we bit-rotate the intermediate value and continue hashing, but with the strict case, when we get a NULL key, we immediately jump to the "jumpdone" step. The problem is the jumpdone step expects the ExprState resnull and resvalue fields to be set (as they would be if we didn't abort hashing early due to the NULL), but when we aborted early, the ExprState fields never got set. This would result in inserting records into the hash table that would never match to any join partner, which is a waste of CPU and memory. Here we fix this by having EEOP_HASHDATUM_FIRST_STRICT and EEOP_HASHDATUM_NEXT32_STRICT populate the ExprState resnull and resvalue fields directly when the value to hash is NULL. Although Hash Agg and Hashed Subplans do use hashing from ExprStates, those were unaffected by this bug, as neither of those uses the STRICT op steps. Thanks to Tomas Vondra for finding the offending commit. Reported-by: Dan Stefura <dstefura@bluecatnetworks.com> Author: David Rowley <dgrowleyml@gmail.com> Discussion: https://postgr.es/m/YQBPR0101MB89738FB972FBD02A3640C6D3D6C92@YQBPR0101MB8973.CANPRD01.PROD.OUTLOOK.COM Backpatch-through: 18
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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/18/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/18/installation.html.
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