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There can never be a need to push the indcheckxmin horizon forward, since any HOT chains that are actually broken with respect to the index must pre-date its original creation. So we can just avoid changing pg_index altogether during a REINDEX operation. This offers a cleaner solution than my previous patch for the problem found a few days ago that we mustn't try to update pg_index while we are reindexing it. System catalog indexes will always be created with indcheckxmin = false during initdb, and with this modified code we should never try to change their pg_index entries. This avoids special-casing system catalogs as the former patch did, and should provide a performance benefit for many cases where REINDEX formerly caused an index to be considered unusable for a short time. Back-patch to 8.3 to cover all versions containing HOT. Note that this patch changes the API for index_build(), but I believe it is unlikely that any add-on code is calling that directly.