mirror of https://github.com/postgres/postgres
Peter Eisentraut
25 years ago
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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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@ -1,107 +0,0 @@ |
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=========== |
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1999 Jul 21 |
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=========== |
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Josef Balatka, <balatka@email.cz> asked us not to remove RECODE and sent me |
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Czech ISO-8859-2 -> WIN-1250 translation table. |
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RECODE is no longer contains just Cyrillic RECODE and will stay in |
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PostgreSQL. |
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He also created some bits of documentation, mostly concerning RECODE - |
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see README.Charsets. |
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=========== |
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1999 Apr 14 |
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=========== |
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Tatsuo Ishii <t-ishii@sra.co.jp> updated Multibyte support extending it |
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to Cyrillic language. Now PostgreSQL supports KOI8-R, WIN-1251, ISO8859-5 |
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and CP866 (ALT) encodings. |
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Short instruction on using this feature follows. Longer discussion of |
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Multibyte support is in README.mb. |
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WARNING! Now with Multibyte support Cyrillic RECODE declared obsolete |
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and will be removed from Postgres. If you are using RECODE consider |
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switching to Multibyte support. |
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Instructions on how to prepare Postgres for Cyrillic Multibyte support. |
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---------------------------------------------------------------------- |
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First, you need to backup all your databases. I recommend to backup the |
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entire Postgres directory, including binaries and libraries - thus you can |
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easily restore if something goes wrong. |
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Dump you data: pg_dumpall > dump.db |
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Stop postmaster. |
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Configure, compile and install Postgres. (I'll mostly talk about KOI8-R |
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encoding, this is just to make examples a little more clear; you can use |
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any supported encoding.) |
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cd src |
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./configure --enable-locale --with-mb=KOI8 |
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make |
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make install |
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Make sure you've backed up your databases. Doublecheck your backup. I |
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really mean it - make regular backups and test your backups sometimes by |
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fake restore. |
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Remove your data directory (better, rename or move it). |
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Run initdb saying your primary encoding: initdb -e KOI8. If you omit |
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encoding, primary encoding from configure will be taken. |
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Start postmaster. |
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Create databases: createdb -e KOI8. Again, you can omit encoding - |
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default encoding will be used. You are not forced to use the same encoding |
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for all your databases - you can create different databases with different |
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encodings. |
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Load your data from the dump you've created: psql < dump.db |
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That's all! Now you are ready to enjoy the full power of Multibyte |
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support. |
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To use Multibyte support you do not need to do something special - just |
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execute your queries. If client program does not set encoding, it will get |
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the data in database encoding. But client may ask Postgres to do automatic |
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server-to-client and client-to-server conversions. There are 2 (two) ways |
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client program declares its encoding: |
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1) client explicitly executes the query SET CLIENT_ENCODING TO 'win'; |
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2) client started with environment variable set. Examples - |
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using sh syntax: |
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PGCLIENTENCODING='win'; export PGCLIENTENCODING |
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using csh syntax: |
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setenv PGCLIENTENCODING 'win' |
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Setting PGCLIENTENCODING even if you use same client encding as the |
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database would omit an overhead of asking the database encoding while |
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initiating the connection, so it is good idea to set it in any case. |
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Now you may run test suite and see Multibyte support in action. Go to |
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.../src/test/locale and run |
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make clean all test-koi2win |
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=========== |
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1998 Nov 20 |
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=========== |
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I extended locale support, originally written by Oleg Bartunov |
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<oleg@sai.msu.su>. Now ORDER BY (if PostgreSQL configured with |
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--enable-locale) uses strcoll() for all text fields: char(n), varchar(n), |
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text. |
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I included test suite .../src/test/locale. I didn't include this in |
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the regression test because not so much people require locale support. Read |
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.../src/test/locale/README for details on the test suite. |
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Many thanks to Oleg Bartunov (oleg@sai.msu.su) and Thomas G. Lockhart |
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(lockhart@alumni.caltech.edu) for hints, tips, help and discussion. |
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Oleg. |
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