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114 lines
4.9 KiB
Plaintext
114 lines
4.9 KiB
Plaintext
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PostgreSQL Charsets README
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Josef Balatka, <balatka@email.cz>
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Draft v0.1, Tue Jul 20 15:49:07 CEST 1999
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This document is a brief overview of the national charsets support
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that PostgreSQL ver. 6.5 has implemented. Various compilation options
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and setup tips are mentioned here to be helpful in the particular use.
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---------------------------------------------------------------------------
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Table of Contents
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1. Locale awareness
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2. Single-byte charsets recoding
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3. Multi-byte support/recoding
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4. Credits
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---------------------------------------------------------------------------
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1. Locale awareness
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PostgreSQL server supports both locale aware and locale not aware
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(default) operational modes. You can determine this mode during the
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configuration stage of the installation with --enable-locale option.
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If you don't use --enable-locale, the multi-language code will not be
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compiled and PostgreSQL will behave as an ASCII compliant application.
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This mode is useful for its speed but only provided that you don't
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have to consider national specific chars.
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With --enable-locale you will get a locale aware server using LC_*
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environment variables to determine how to process national specifics.
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In this case strcoll(3) and similar functions are used internally
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so speed is somewhat lower.
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Notice here that --enable-locale is sufficient when all your clients
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use the same single-byte encoding as the database server does.
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When your clients use encoding different from the server than you have
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to use, moreover, --enable-recode or --with-mb=<encoding> options on
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the server side or a particular client that does recoding itself (e.g.
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there exists a PostgreSQL ODBC driver for Win32 with various Cyrillic
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encoding capability). Option --with-mb=<encoding> is necessary for the
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multi-byte charsets support.
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2. Single-byte charsets recoding
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You can set up this feature with --enable-recode option. This option
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is described as 'enable Cyrillic recode support' which doesn't express
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all its power. It can be used for *any* single-byte charset recoding.
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This method uses charset.conf file located in the $PGDATA directory.
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It's a typical configuration text file where spaces and newlines
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separate items and records and # specifies comments. Three keywords
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with the following syntax are recognized here:
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BaseCharset <server_charset>
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RecodeTable <from_charset> <to_charset> <file_name>
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HostCharset <host_spec> <host_charset>
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BaseCharset defines encoding of the database server. All charset
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names are only used for mapping inside the charset.conf so you can
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freely use typing-friendly names.
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RecodeTable records specify translation table between server and client.
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The file name is relative to the $PGDATA directory. Table file format
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is very simple. There are no keywords and characters are represented by
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a pair of decimal or hexadecimal (0x prefixed) values on single lines:
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<char_value> <translated_char_value>
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HostCharset records define IP address and charset. You can use a single
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IP address, an IP mask range starting from the given address or an IP
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interval (e.g. 127.0.0.1, 192.168.1.100/24, 192.168.1.20-192.168.1.40)
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The charset.conf is always processed up to the end, so you can easily
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specify exceptions from the previous rules. In the src/data you will
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find charset.conf example and a few recoding tables.
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As this solution is based on the client's IP address / charset mapping
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there are obviously some restrictions as well. You can't use different
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encoding on the same host at the same time. It's also inconvenient when
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you boot your client hosts into more operating systems.
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Nevertheless, when these restrictions are not limiting and you don't
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need multi-byte chars than it's a simple and effective solution.
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3. Multi-byte support/recoding
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It's a new generation of charset encoding in PostgreSQL designed as a
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more complex solution supporting both single-byte and multi-byte chars.
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You can set up this feature with --with-mb=<encoding> option.
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There is no IP mapping file and recoding is controlled through the new
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SQL statements. Recoding tables are included in the code. Many national
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charsets are already supported and further will follow.
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See doc/README.mb, doc/README.mb.jp to get detailed instruction on how
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to use the multibyte support. In the file doc/README.locale there is
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a particular instruction on usage of the multibyte support with Cyrillic.
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4. Credits
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I'd like to thank the PostgreSQL development team and all contributors
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for creating PostgreSQL. Thanks to Oleg Bartunov, Oleg Broytmann and
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Tatsuo Ishii for opening the door into the multi-language world.
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