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If MERGE attempts an UPDATE or DELETE on a table with BEFORE ROW triggers, or a cross-partition UPDATE (with or without triggers), and a concurrent UPDATE or DELETE happens, the merge code would fail. In some cases this would lead to a crash, while in others it would cause the wrong merge action to be executed, or no action at all. The immediate cause of the crash was the trigger code calling ExecGetUpdateNewTuple() as part of the EPQ mechanism, which fails because during a merge ri_projectNew is NULL, since merge has its own per-action projection information, which ExecGetUpdateNewTuple() knows nothing about. Fix by arranging for the trigger code to exit early, returning the TM_Result and TM_FailureData information, if a concurrent modification is detected, allowing the merge code to do the necessary EPQ handling in its own way. Similarly, prevent the cross-partition update code from doing any EPQ processing for a merge, allowing the merge code to work out what it needs to do. This leads to a number of simplifications in nodeModifyTable.c. Most notably, the ModifyTableContext->GetUpdateNewTuple() callback is no longer needed, and mergeGetUpdateNewTuple() can be deleted, since there is no longer any requirement for get-update-new-tuple during a merge. Similarly, ModifyTableContext->cpUpdateRetrySlot is no longer needed. Thus ExecGetUpdateNewTuple() and the retry_slot handling of ExecCrossPartitionUpdate() can be restored to how they were in v14, before the merge code was added, and ExecMergeMatched() no longer needs any special-case handling for cross-partition updates. While at it, tidy up ExecUpdateEpilogue() a bit, making it handle recheckIndexes locally, rather than passing it in as a parameter, ensuring that it is freed properly. This dates back to when it was split off from ExecUpdate() to support merge. Per bug #17809 from Alexander Lakhin, and follow-up investigation of bug #17792, also from Alexander Lakhin. Back-patch to v15, where MERGE was introduced, taking care to preserve backwards-compatibility of the trigger API in v15 for any extensions that might use it. Discussion: https://postgr.es/m/17809-9e6650bef133f0fe%40postgresql.org https://postgr.es/m/17792-0f89452029662c36%40postgresql.org
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/.