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inserting a materialize node above an inner-side sort node, when the sort is expected to spill to disk. (The materialize protects the sort from having to support mark/restore, allowing it to do its final merge pass on-the-fly.) We neglected to teach cost_mergejoin about that hack, so it was failing to include the materialize's costs in the estimated cost of the mergejoin. The materialize's costs are generally going to be pretty negligible in comparison to the sort's, so this is only a small error and probably not worth back-patching; but it's still wrong. In the similar case where a materialize is inserted to protect an inner-side node that can't do mark/restore at all, it's still true that the materialize should not spill to disk, and so we should cost it cheaply rather than expensively. Noted while thinking about a question from Tom Raney. |
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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. Changes between all PostgreSQL releases are recorded in the file HISTORY. 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/.