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sequence, even when the input "tour" doesn't lead directly to such a sequence. The stack logic that was added in 2004 only supported cases where relations that had to be joined to each other (due to join order restrictions) were adjacent in the tour. However, relying on a random search to figure that out is tremendously inefficient in large join problems, and could even fail completely (leading to "failed to make a valid plan" errors) if random_init_pool ran out of patience. It seems better to make the tour-to-plan transformation a little bit fuzzier so that every tour can form a legal plan, even though this means that apparently different tours will sometimes yield the same plan. In the same vein, get rid of the logic that knew that tours (a,b,c,d,...) are the same as tours (b,a,c,d,...), and therefore insisted the latter are invalid. The chance of generating two tours that differ only in this way isn't that high, and throwing out 50% of possible tours to avoid such duplication seems more likely to waste valuable genetic- refinement generations than to do anything useful. This leaves us with no cases in which geqo_eval will deem a tour invalid, so get rid of assorted kluges that tried to deal with such cases, in particular the undocumented assumption that DBL_MAX is an impossible plan cost. This is all per testing of Robert Haas' lets-remove-the-collapse-limits patch. That idea has crashed and burned, at least for now, but we still got something useful out of it. It's possible we should back-patch this change, since the "failed to make a valid plan" error can happen in existing releases; but I'd rather not until it has gotten more testing. |
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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/.