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This code could produce very poor results when asked to highlight a string based on a query using phrase-match operators. The root cause is that hlCover(), which is supposed to find a minimal substring that matches the query, was written assuming that word position is not significant. I'm only 95% convinced that its algorithm was correct even for plain AND/OR queries; but it definitely fails completely for phrase matches, causing it to possibly not identify a cover string at all. Hence, rewrite hlCover() with a less-tense algorithm that just tries all the possible substrings, earlier and shorter ones first. (This is not as bad as it sounds performance-wise, because all of the string matching has been done already: the repeated tsquery match checks boil down to pointer comparisons.) Unfortunately, since that approach produces more candidate cover strings than before, it also exposes that there were bugs in the heuristics in mark_hl_words() for selecting a best cover string. Fixes there include: * Do not apply the ShortWord filter to words that appear in the query. * Remove a misguided optimization for quickly rejecting a cover. * Fix order-of-operation bug that could cause computation of a wrong figure of merit (poslen) when shortening a cover. * Change the preference rule so that candidate headlines that do not include their whole cover string (after MaxWords trimming) are lowest priority, since they may not actually satisfy the user's query. This results in some changes in existing regression test cases, but they all seem reasonable. Note in particular that the tests involving strings like "1 2 3" were previously being affected by the ShortWord filter, masking the normal matching behavior. Per bug #16345 from Augustinas Jokubauskas; the new test cases are based on that example. Back-patch to 9.6 where phrase search was added to tsquery. Discussion: https://postgr.es/m/16345-2e0cf5cddbdcd3b4@postgresql.org |
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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: https://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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.