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When instrumenting a MERGE command containing both WHEN NOT MATCHED BY SOURCE and WHEN NOT MATCHED BY TARGET actions using EXPLAIN ANALYZE, a concurrent update of the target relation could lead to an Assert failure in show_modifytable_info(). In a non-assert build, this would lead to an incorrect value for "skipped" tuples in the EXPLAIN output, rather than a crash. This could happen if the concurrent update caused a matched row to no longer match, in which case ExecMerge() treats the single originally matched row as a pair of not matched rows, and potentially executes 2 not-matched actions for the single source row. This could then lead to a state where the number of rows processed by the ModifyTable node exceeds the number of rows produced by its source node, causing "skipped_path" in show_modifytable_info() to be negative, triggering the Assert. Fix this in ExecMergeMatched() by incrementing the instrumentation tuple count on the source node whenever a concurrent update of this kind is detected, if both kinds of merge actions exist, so that the number of source rows matches the number of actions potentially executed, and the "skipped" tuple count is correct. Back-patch to v17, where support for WHEN NOT MATCHED BY SOURCE actions was introduced. Bug: #19111 Reported-by: Dilip Kumar <dilipbalaut@gmail.com> Author: Dean Rasheed <dean.a.rasheed@gmail.com> Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com> Discussion: https://postgr.es/m/19111-5b06624513d301b3@postgresql.org Backpatch-through: 17 |
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