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We can do this without creating an API break for estimation functions by passing the collation using the existing fmgr functionality for passing an input collation as a hidden parameter. The need for this was foreseen at the outset, but we didn't get around to making it happen in 9.1 because of the decision to sort all pg_statistic histograms according to the database's default collation. That meant that selectivity estimators generally need to use the default collation too, even if they're estimating for an operator that will do something different. The reason it's suddenly become more interesting is that regexp interpretation also uses a collation (for its LC_TYPE not LC_COLLATE property), and we no longer want to use the wrong collation when examining regexps during planning. It's not that the selectivity estimate is likely to change much from this; rather that we are thinking of caching compiled regexps during planner estimation, and we won't get the intended benefit if we cache them with a different collation than the executor will use. Back-patch to 9.1, both because the regexp change is likely to get back-patched and because we might as well get this right in all collation-supporting branches, in case any third-party code wants to rely on getting the collation. The patch turns out to be minuscule now that I've done it ... |
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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/.