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d4b5d4cadd
It's currently necessary to take a heavyweight lock when scanning a hash bucket, but pgstattuple only examines individual pages, so it doesn't need to do this. If, for some hypothetical reason, it did need to do any heavyweight locking here, this logic would probably still be incorrect, because most of the locks that it is taking are meaningless. Only a heavyweight lock on a primary bucket page has any meaning, but this takes heavyweight locks on all pages regardless of function - and in particular overflow pages, where you might imagine that we'd want to lock the primary bucket page if we needed to lock anything at all. This is arguably a bug that has existed since this code was added in commit dab42382f483c3070bdce14a4d93c5d0cf61e82b, but I'm not going to bother back-patching it because in most cases the only consequence is that running pgstattuple() on a hash index is a little slower than it otherwise might be, which is no big deal. Extracted from a vastly larger patch by Amit Kapila which heavyweight locking for hash indexes entirely; analysis of why this can be done independently of the rest by me.
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.