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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
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.