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Previously, the core scanner's yy_transition[] array had 37045 elements. Since that number is larger than INT16_MAX, Flex generated the array to contain 32-bit integers. By reimplementing some of the bulkier scanner rules, this patch reduces the array to 20495 elements. The much smaller total length, combined with the consequent use of 16-bit integers for the array elements reduces the binary size by over 200kB. This was accomplished in two ways: 1. Consolidate handling of quote continuations into a new start condition, rather than duplicating that logic for five different string types. 2. Treat Unicode strings and identifiers followed by a UESCAPE sequence as three separate tokens, rather than one. The logic to de-escape Unicode strings is moved to the filter code in parser.c, which already had the ability to provide special processing for token sequences. While we could have implemented the conversion in the grammar, that approach was rejected for performance and maintainability reasons. Performance in microbenchmarks of raw parsing seems equal or slightly faster in most cases, and it's reasonable to expect that in real-world usage (with more competition for the CPU cache) there will be a larger win. The exception is UESCAPE sequences; lexing those is about 10% slower, primarily because the scanner now has to be called three times rather than one. This seems acceptable since that feature is very rarely used. The psql and epcg lexers are likewise modified, primarily because we want to keep them all in sync. Since those lexers don't use the space-hogging -CF option, the space savings is much less, but it's still good for perhaps 10kB apiece. While at it, merge the ecpg lexer's handling of C-style comments used in SQL and in C. Those have different rules regarding nested comments, but since we already have the ability to keep track of the previous start condition, we can use that to handle both cases within a single start condition. This matches the core scanner more closely. John Naylor Discussion: https://postgr.es/m/CACPNZCvaoa3EgVWm5yZhcSTX6RAtaLgniCPcBVOCwm8h3xpWkw@mail.gmail.com |
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README
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/.