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a5fc46414d
When we decide we need to make a derived clause equating a.x and b.y, we already will re-use a previously-made clause "a.x = b.y". But we might instead have "b.y = a.x", which is perfectly usable because equivclass.c has never promised anything about the operand order in clauses it builds. Saving construction of a new RestrictInfo doesn't matter all that much in itself --- but because we cache selectivity estimates and so on per-RestrictInfo, there's a possibility of saving a fair amount of duplicative effort downstream. Hence, check for commutative matches as well as direct ones when seeing if we have a pre-existing clause. This changes the visible clause order in several regression test cases, but they're all clearly-insignificant changes. Checking for the reverse operand order is simple enough, but if we wanted to check for operator OID match we'd need to call get_commutator here, which is not so cheap. I concluded that we don't really need the operator check anyway, so I just removed it. It's unlikely that an opfamily contains more than one applicable operator for a given pair of operand datatypes; and if it does they had better give the same answers, so there seems little need to insist that we use exactly the one select_equality_operator chose. Using the current core regression suite as a test case, I see this change reducing the number of new join clauses built by create_join_clause from 9673 to 5142 (out of 26652 calls). So not quite 50% savings, but pretty close to it. Discussion: https://postgr.es/m/78062.1666735746@sss.pgh.pa.us
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.