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a0efda88a6
Somebody extended search_plan_tree() to treat MergeAppend exactly like Append, which is 100% wrong, because unlike Append we can't assume that only one input node is actively returning tuples. Hence a cursor using a MergeAppend across a UNION ALL or inheritance tree could falsely match a WHERE CURRENT OF query at a row that isn't actually the cursor's current output row, but coincidentally has the same TID (in a different table) as the current output row. Delete the faulty code; this means that such a case will now return an error like 'cursor "foo" is not a simply updatable scan of table "bar"', instead of silently misbehaving. Users should not find that surprising though, as the same cursor query could have failed that way already depending on the chosen plan. (It would fail like that if the sort were done with an explicit Sort node instead of MergeAppend.) Expand the clearly-inadequate commentary to be more explicit about what this code is doing, in hopes of forestalling future mistakes. It's been like this for awhile, so back-patch to all supported branches. Discussion: https://postgr.es/m/482865.1611075182@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/.