b746d0c32d
While poking at David Kubečka's issue I noticed an ancient logic error in get_loop_count(): it used 1.0 as a "no data yet" indicator, but since that is actually a valid rowcount estimate, this doesn't work. If we have one input relation with 1.0 as rowcount and then another one with a larger rowcount, we should use 1.0 as the result, but we picked the larger rowcount instead. (I think when I coded this, I recognized the conflict, but mistakenly thought that the logic would pick the desired count anyway.) Fixing this changed the plan for one existing regression test case. Since the point of that test is to exercise creation of a particular shape of nestloop plan, I tweaked the query a little bit so it still results in the same plan choice. This is definitely a bug, but I'm hesitant to back-patch since it might change plan choices unexpectedly, and anyway failure to implement a heuristic precisely as intended is a pretty low-grade bug. |
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README
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/.