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Commit 857f9c36cda, which taught nbtree VACUUM to avoid unnecessary index scans, bumped the nbtree version number from 2 to 3, while adding the ability for nbtree indexes to be upgraded on-the-fly. Various assertions that assumed that an nbtree index was always on version 2 had to be changed to accept any supported version (version 2 or 3 on Postgres 11). However, a few assertions were missed in the initial commit, all of which were in code paths that cache a local copy of the metapage metadata, where the index had been expected to be on the current version (no longer version 2) as a generic sanity check. Rather than simply update the assertions, follow-up commit 0a64b45152b intentionally made the metapage caching code update the per-backend cached metadata version without changing the on-disk version at the same time. This could even happen when the planner needed to determine the height of a B-Tree for costing purposes. The assertions only fail on Postgres v12 when upgrading from v10, because they were adjusted to use the authoritative shared memory metapage by v12's commit dd299df8. To fix, remove the cache-only upgrade mechanism entirely, and update the assertions themselves to accept any supported version (go back to using the cached version in v12). The fix is almost a full revert of commit 0a64b45152b on the v11 branch. VACUUM only considers the authoritative metapage, and never bothers with a locally cached version, whereas everywhere else isn't interested in the metapage fields that were added by commit 857f9c36cda. It seems unlikely that this bug has affected any user on v11. Reported-By: Christoph Berg Bug: #15896 Discussion: https://postgr.es/m/15896-5b25e260fdb0b081%40postgresql.org Backpatch: 11-, where VACUUM was taught to avoid unnecessary index scans.
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/.