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While trying to plan a partitionwise join, we may be faced with cases where one or both input partitions for a particular segment of the join have been pruned away. In HEAD and v11, this is problematic because earlier processing didn't bother to make a pruned RelOptInfo fully valid. With an upcoming patch to make partition pruning more efficient, this'll be even more problematic because said RelOptInfo won't exist at all. The existing code attempts to deal with this by retroactively making the RelOptInfo fully valid, but that causes crashes under GEQO because join planning is done in a short-lived memory context. In v11 we could probably have fixed this by switching to the planner's main context while fixing up the RelOptInfo, but that idea doesn't scale well to the upcoming patch. It would be better not to mess with the base-relation data structures during join planning, anyway --- that's just a recipe for order-of-operations bugs. In many cases, though, we don't actually need the child RelOptInfo, because if the input is certainly empty then the join segment's result is certainly empty, so we can skip making a join plan altogether. (The existing code ultimately arrives at the same conclusion, but only after doing a lot more work.) This approach works except when the pruned-away partition is on the nullable side of a LEFT, ANTI, or FULL join, and the other side isn't pruned. But in those cases the existing code leaves a lot to be desired anyway --- the correct output is just the result of the unpruned side of the join, but we were emitting a useless outer join against a dummy Result. Pending somebody writing code to handle that more nicely, let's just abandon the partitionwise-join optimization in such cases. When the modified code skips making a join plan, it doesn't make a join RelOptInfo either; this requires some upper-level code to cope with nulls in part_rels[] arrays. We would have had to have that anyway after the upcoming patch. Back-patch to v11 since the crash is demonstrable there. Discussion: https://postgr.es/m/8305.1553884377@sss.pgh.pa.us |
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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/.