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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 dab42382f4, 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.