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In commit b514a7460d, I changed the planner
so that it would allow nestloop paths to remain partially parameterized,
ie the inner relation might need parameters from both the current outer
relation and some upper-level outer relation. That's fine so long as we're
talking about distinct parameters; but the patch also allowed creation of
nestloop paths for cases where the inner relation's parameter was a
PlaceHolderVar whose eval_at set included the current outer relation and
some upper-level one. That does *not* work.
In principle we could allow such a PlaceHolderVar to be evaluated at the
lower join node using values passed down from the upper relation along with
values from the join's own outer relation. However, nodeNestloop.c only
supports simple Vars not arbitrary expressions as nestloop parameters.
createplan.c is also a few bricks shy of being able to handle such cases;
it misplaces the PlaceHolderVar parameters in the plan tree, which is why
the visible symptoms of this bug are "plan should not reference subplan's
variable" and "failed to assign all NestLoopParams to plan nodes" planner
errors.
Adding the necessary complexity to make this work doesn't seem like it
would be repaid in significantly better plans, because in cases where such
a PHV exists, there is probably a corresponding join order constraint that
would allow a good plan to be found without using the star-schema exception.
Furthermore, adding complexity to nodeNestloop.c would create a run-time
penalty even for plans where this whole consideration is irrelevant.
So let's just reject such paths instead.
Per fuzz testing by Andreas Seltenreich; the added regression test is based
on his example query. Back-patch to 9.2, like the previous patch.
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/.