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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.
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: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.