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After detecting a sub-match "dissect" failure (i.e., a backref match failure) in the i'th sub-match of an iteration node, we should proceed by adjusting the attempted length of the i'th submatch. As coded, though, these functions changed the attempted length of the *last* sub-match, and only after exhausting all possibilities for that would they back up to adjust the next-to-last sub-match, and then the second-from-last, etc; all of which is wasted effort, since only changing the start or length of the i'th sub-match can possibly make it succeed. This oversight creates the possibility for exponentially bad performance. Fortunately the problem is masked in most cases by optimizations or constraints applied elsewhere; which explains why we'd not noticed it before. But it is possible to reach the problem with fairly simple, if contrived, regexps. Oversight in my commit 173e29aa5. That's pretty ancient now, so back-patch to all supported branches. Discussion: https://postgr.es/m/1808998.1629412269@sss.pgh.pa.us
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/.