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Instead of having left and right child links in subre structs, have a single child link plus a sibling link. Multiple children of a tree node are now reached by chasing the sibling chain. The beneficiary of this is alternation tree nodes. A regular expression with N (>1) branches is now represented by one alternation node with N children, rather than a tree that includes N alternation nodes as well as N children. While the old representation didn't really cost anything extra at execution time, it was pretty horrid for compilation purposes, because each of the alternation nodes had its own NFA, which we were too stupid not to separately optimize. (To make matters worse, all of those NFAs described the entire alternation pattern, not just the portion of it that one might expect from the tree structure.) We continue to require concatenation nodes to have exactly two children. This data structure is now prepared to support more, but the executor's logic would need some careful redesign, and it's not clear that a lot of benefit could be had. This is part of a patch series that in total reduces the regex engine's runtime by about a factor of four on a large corpus of real-world regexes. Patch by me, reviewed by Joel Jacobson Discussion: https://postgr.es/m/1340281.1613018383@sss.pgh.pa.us |
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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/.