12.7. Configuration Example
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## 12.7. Configuration Example #

A text search configuration specifies all options necessary to transform a document into a `tsvector`: the parser to use to break text into tokens, and the dictionaries to use to transform each token into a lexeme. Every call of `to_tsvector` or `to_tsquery` needs a text search configuration to perform its processing. The configuration parameter default_text_search_config specifies the name of the default configuration, which is the one used by text search functions if an explicit configuration parameter is omitted. It can be set in `postgresql.conf`, or set for an individual session using the `SET` command.

Several predefined text search configurations are available, and you can create custom configurations easily. To facilitate management of text search objects, a set of SQL commands is available, and there are several psql commands that display information about text search objects (Section 12.10).

As an example we will create a configuration `pg`, starting by duplicating the built-in `english` configuration:

    CREATE TEXT SEARCH CONFIGURATION public.pg ( COPY = pg_catalog.english );

We will use a PostgreSQL-specific synonym list and store it in `$SHAREDIR/tsearch_data/pg_dict.syn`. The file contents look like:

    postgres    pg
    pgsql       pg
    postgresql  pg

We define the synonym dictionary like this:

    CREATE TEXT SEARCH DICTIONARY pg_dict (
        TEMPLATE = synonym,
        SYNONYMS = pg_dict
    );

Next we register the Ispell dictionary `english_ispell`, which has its own configuration files:

    CREATE TEXT SEARCH DICTIONARY english_ispell (
        TEMPLATE = ispell,
        DictFile = english,
        AffFile = english,
        StopWords = english
    );

Now we can set up the mappings for words in configuration `pg`:

    ALTER TEXT SEARCH CONFIGURATION pg
        ALTER MAPPING FOR asciiword, asciihword, hword_asciipart,
                          word, hword, hword_part
        WITH pg_dict, english_ispell, english_stem;

We choose not to index or search some token types that the built-in configuration does handle:

    ALTER TEXT SEARCH CONFIGURATION pg
        DROP MAPPING FOR email, url, url_path, sfloat, float;

Now we can test our configuration:

    SELECT * FROM ts_debug('public.pg', '
    PostgreSQL, the highly scalable, SQL compliant, open source object-relational
    database management system, is now undergoing beta testing of the next
    version of our software.
    ');

The next step is to set the session to use the new configuration, which was created in the `public` schema:

    => \dF
       List of text search configurations
     Schema  | Name | Description
    ---------+------+-------------
     public  | pg   |

    SET default_text_search_config = 'public.pg';
    SET

    SHOW default_text_search_config;
     default_text_search_config
    ----------------------------
     public.pg

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