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Given a permanent relation rewritten in the current transaction, the old_snapshot_threshold mechanism assumed the relation had never been subject to early pruning. Hence, a query could fail to report "snapshot too old" when the rewrite followed an early truncation. ALTER TABLE SET TABLESPACE is probably the only rewrite mechanism capable of exposing this bug. REINDEX sets indcheckxmin, avoiding the problem. CLUSTER has zeroed page LSNs since before old_snapshot_threshold existed, so old_snapshot_threshold has never cooperated with it. ALTER TABLE ... SET DATA TYPE makes the table look empty to every past snapshot, which is strictly worse. Back-patch to v13, where commit c6b92041d38512a4176ed76ad06f713d2e6c01a8 broke this. Kyotaro Horiguchi and Noah Misch Discussion: https://postgr.es/m/20210113.160705.2225256954956139776.horikyota.ntt@gmail.com
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/.