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In a case where we have multiple relation-scan nodes in a cursor plan, such as a scan of an inheritance tree, it's possible to fetch from a given scan node, then rewind the cursor and fetch some row from an earlier scan node. In such a case, execCurrent.c mistakenly thought that the later scan node was still active, because ExecReScan hadn't done anything to make it look not-active. We'd get some sort of failure in the case of a SeqScan node, because the node's scan tuple slot would be pointing at a HeapTuple whose t_self gets reset to invalid by heapam.c. But it seems possible that for other relation scan node types we'd actually return a valid tuple TID to the caller, resulting in updating or deleting a tuple that shouldn't have been considered current. To fix, forcibly clear the ScanTupleSlot in ExecScanReScan. Another issue here, which seems only latent at the moment but could easily become a live bug in future, is that rewinding a cursor does not necessarily lead to *immediately* applying ExecReScan to every scan-level node in the plan tree. Upper-level nodes will think that they can postpone that call if their child node is already marked with chgParam flags. I don't see a way for that to happen today in a plan tree that's simple enough for execCurrent.c's search_plan_tree to understand, but that's one heck of a fragile assumption. So, add some logic in search_plan_tree to detect chgParam flags being set on nodes that it descended to/through, and assume that that means we should consider lower scan nodes to be logically reset even if their ReScan call hasn't actually happened yet. Per bug #15395 from Matvey Arye. This has been broken for a long time, so back-patch to all supported branches. Discussion: https://postgr.es/m/153764171023.14986.280404050547008575@wrigleys.postgresql.org |
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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/.