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ExecInitCteScan supposed that it didn't have to do anything to the extra tuplestore read pointer it gets from tuplestore_alloc_read_pointer. However, it needs this read pointer to be positioned at the start of the tuplestore, while tuplestore_alloc_read_pointer is actually defined as cloning the current position of read pointer 0. In normal situations that accidentally works because we initialize the whole plan tree at once, before anything gets read. But it fails in an EvalPlanQual recheck, as illustrated in bug #14328 from Dima Pavlov. To fix, just forcibly rewind the pointer after tuplestore_alloc_read_pointer. The cost of doing so is negligible unless the tuplestore is already in TSS_READFILE state, which wouldn't happen in normal cases. We could consider altering tuplestore's API to make that case cheaper, but that would make for a more invasive back-patch and it doesn't seem worth it. This has been broken probably for as long as we've had CTEs, so back-patch to all supported branches. Discussion: <32468.1474548308@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: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.