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pgstattuple checks the state of the pages retrieved for gist and hash using some check functions from each index AM, respectively gistcheckpage() and _hash_checkpage(). When these are called, they would fail when bumping on data that is found as incorrect (like opaque area size not matching, or empty pages), contrary to btree that simply discards these cases and continues to aggregate data. Zero pages can happen after a crash, with these AMs being able to do an internal cleanup when these are seen. Also, sporadic failures are annoying when doing for example a large-scale diagnostic query based on pgstattuple with a join of pg_class, as it forces one to use tricks like quals to discard hash or gist indexes, or use a PL wrapper able to catch errors. This commit changes the reports generated for btree, gist and hash to be more user-friendly; - When seeing an empty page, report it as free space. This new rule applies to gist and hash, and already applied to btree. - For btree, a check based on the size of BTPageOpaqueData is added. - For gist indexes, gistcheckpage() is not called anymore, replaced by a check based on the size of GISTPageOpaqueData. - For hash indexes, instead of _hash_getbuf_with_strategy(), use a direct call to ReadBufferExtended(), coupled with a check based on HashPageOpaqueData. The opaque area size check was already used. - Pages that do not match these criterias are discarded from the stats reports generated. There have been a couple of bug reports over the years that complained about the current behavior for hash and gist, as being not that useful, with nothing being done about it. Hence this change is backpatched down to v13. Reported-by: Noah Misch <noah@leadboat.com> Author: Nitin Motiani <nitinmotiani@google.com> Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com> Discussion: https://postgr.es/m/CAH5HC95gT1J3dRYK4qEnaywG8RqjbwDdt04wuj8p39R=HukayA@mail.gmail.com Backpatch-through: 13
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/.