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If you have a GIN query like "rare & frequent", we currently fetch all the items that match either rare or frequent, call the consistent function for each item, and let the consistent function filter out items that only match one of the terms. However, if we can deduce that "rare" must be present for the overall qual to be true, we can scan all the rare items, and for each rare item, skip over to the next frequent item with the same or greater TID. That greatly speeds up "rare & frequent" type queries. To implement that, introduce the concept of a tri-state consistent function, where the 3rd value is MAYBE, indicating that we don't know if that term is present. Operator classes only provide a boolean consistent function, so we simulate the tri-state consistent function by calling the boolean function several times, with the MAYBE arguments set to all combinations of TRUE and FALSE. Testing all combinations is only feasible for a small number of MAYBE arguments, but it is envisioned that we'll provide a way for operator classes to provide a native tri-state consistent function, which can be much more efficient. But that is not included in this patch. We were already using that trick to for lossy pages, calling the consistent function with the lossy entry set to TRUE and FALSE. Now that we have the tri-state consistent function, use it for lossy pages too. Alexander Korotkov, with fair amount of refactoring by me. |
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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/.