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5f6f840e93
to suppress zero-padding of "name" entries in indexes. The alignment change is unlikely to save any space, but it is really needed anyway to make the world safe for our widespread practice of passing plain old C strings to functions that are declared as taking Name. In the previous coding, the C compiler was entitled to assume that a Name pointer was word-aligned; but we were failing to guarantee that. I think the reason we'd not seen failures is that usually the only thing that gets done with such a pointer is strcmp(), which is hard to optimize in a way that exploits word-alignment. Still, some enterprising compiler guy will probably think of a way eventually, or we might change our code in a way that exposes more-obvious optimization opportunities. The padding change is accomplished in one-liner fashion by declaring the "name" index opclasses to use storage type "cstring" in pg_opclass.h. Normally btree and hash don't allow a nondefault storage type, because they don't have any provisions for converting the input datum to another type. However, because name and cstring are effectively the same thing except for padding, no conversion is needed --- we only need index_form_tuple() to treat the datum as being cstring not name, and this is sufficient. This seems to make for about a one-third reduction in the typical sizes of system catalog indexes that involve "name" columns, of which we have many. These two changes are only weakly related, but the alignment change makes me feel safer that the padding change won't introduce problems, so I'm committing them together. |
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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/.