3aee628370
One mechanism we have for implementing semi-joins is to de-duplicate the output of the RHS and then treat the join as a plain inner join. Initial construction of the join's SpecialJoinInfo identifies the RHS columns that need to be de-duplicated, but later we may find that some of those don't need to be handled explicitly, either because they're known to be constant or because they are redundant with some previous column. Up to now, while sort-based de-duplication handled such cases well, hash-based de-duplication didn't: we'd still hash on all of the originally-identified columns. This is probably not a very big deal performance-wise, but in the wake of commit a3179ab69 it can cause planner errors. That happens when join elimination causes recalculation of variables' attr_needed bitmapsets, and we decide that a variable mentioned in a semijoin clause doesn't need to be propagated up to the join level anymore. There are a number of ways we could slice the blame for this, but the only fix that doesn't result in pessimizing plans for loosely-related cases is to be more careful about not hashing columns we don't actually need to de-duplicate. We can install that consideration into create_unique_paths in master, or the predecessor code in create_unique_path in v18, without much refactoring. (As follow-up work, it might be a good idea to look at more-invasive refactoring, in hopes of preventing other bugs in this area. But with v18 release so close, there's not time for that now, nor would we be likely to want to put such refactoring into v18 anyway.) Reported-by: Sergey Soloviev <sergey.soloviev@tantorlabs.ru> Diagnosed-by: Richard Guo <guofenglinux@gmail.com> Author: Tom Lane <tgl@sss.pgh.pa.us> Reviewed-by: Richard Guo <guofenglinux@gmail.com> Discussion: https://postgr.es/m/1fd1a421-4609-4d46-a1af-ab74d5de504a@tantorlabs.ru 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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