12.8. Testing and Debugging Text Search
The behavior of a custom text search configuration can easily become confusing. The functions described in this section are useful for testing text search objects. You can test a complete configuration, or test parsers and dictionaries separately.
12.8.1. Configuration Testing
The function ts_debug
allows easy testing of a text search configuration.
ts_debug([config
regconfig
, ]document
text
, OUTalias
text
, OUTdescription
text
, OUTtoken
text
, OUTdictionaries
regdictionary[]
, OUTdictionary
regdictionary
, OUTlexemes
text[]
) returns setof record
ts_debug
displays information about every token of document
as produced by the parser and processed by the configured dictionaries. It uses the configuration specified by config
, or default_text_search_config
if that argument is omitted.
ts_debug
returns one row for each token identified in the text by the parser. The columns returned are
alias
text
— short name of the token typedescription
text
— description of the token typetoken
text
— text of the tokendictionaries
regdictionary[]
— the dictionaries selected by the configuration for this token typedictionary
regdictionary
— the dictionary that recognized the token, orNULL
if none didlexemes
text[]
— the lexeme(s) produced by the dictionary that recognized the token, orNULL
if none did; an empty array ({}
) means it was recognized as a stop word
Here is a simple example:
SELECT * FROM ts_debug('english', 'a fat cat sat on a mat - it ate a fat rats'); alias | description | token | dictionaries | dictionary | lexemes -----------+-----------------+-------+----------------+--------------+--------- asciiword | Word, all ASCII | a | {english_stem} | english_stem | {} blank | Space symbols | | {} | | asciiword | Word, all ASCII | fat | {english_stem} | english_stem | {fat} blank | Space symbols | | {} | | asciiword | Word, all ASCII | cat | {english_stem} | english_stem | {cat} blank | Space symbols | | {} | | asciiword | Word, all ASCII | sat | {english_stem} | english_stem | {sat} blank | Space symbols | | {} | | asciiword | Word, all ASCII | on | {english_stem} | english_stem | {} blank | Space symbols | | {} | | asciiword | Word, all ASCII | a | {english_stem} | english_stem | {} blank | Space symbols | | {} | | asciiword | Word, all ASCII | mat | {english_stem} | english_stem | {mat} blank | Space symbols | | {} | | blank | Space symbols | - | {} | | asciiword | Word, all ASCII | it | {english_stem} | english_stem | {} blank | Space symbols | | {} | | asciiword | Word, all ASCII | ate | {english_stem} | english_stem | {ate} blank | Space symbols | | {} | | asciiword | Word, all ASCII | a | {english_stem} | english_stem | {} blank | Space symbols | | {} | | asciiword | Word, all ASCII | fat | {english_stem} | english_stem | {fat} blank | Space symbols | | {} | | asciiword | Word, all ASCII | rats | {english_stem} | english_stem | {rat}
For a more extensive demonstration, we first create a public.english
configuration and Ispell dictionary for the English language:
CREATE TEXT SEARCH CONFIGURATION public.english ( COPY = pg_catalog.english ); CREATE TEXT SEARCH DICTIONARY english_ispell ( TEMPLATE = ispell, DictFile = english, AffFile = english, StopWords = english ); ALTER TEXT SEARCH CONFIGURATION public.english ALTER MAPPING FOR asciiword WITH english_ispell, english_stem;
SELECT * FROM ts_debug('public.english', 'The Brightest supernovaes'); alias | description | token | dictionaries | dictionary | lexemes -----------+-----------------+-------------+-------------------------------+----------------+------------- asciiword | Word, all ASCII | The | {english_ispell,english_stem} | english_ispell | {} blank | Space symbols | | {} | | asciiword | Word, all ASCII | Brightest | {english_ispell,english_stem} | english_ispell | {bright} blank | Space symbols | | {} | | asciiword | Word, all ASCII | supernovaes | {english_ispell,english_stem} | english_stem | {supernova}
In this example, the word Brightest
was recognized by the parser as an ASCII word
(alias asciiword
). For this token type the dictionary list is english_ispell
and english_stem
. The word was recognized by english_ispell
, which reduced it to the noun bright
. The word supernovaes
is unknown to the english_ispell
dictionary so it was passed to the next dictionary, and, fortunately, was recognized (in fact, english_stem
is a Snowball dictionary which recognizes everything; that is why it was placed at the end of the dictionary list).
The word The
was recognized by the english_ispell
dictionary as a stop word (Section 12.6.1) and will not be indexed. The spaces are discarded too, since the configuration provides no dictionaries at all for them.
You can reduce the width of the output by explicitly specifying which columns you want to see:
SELECT alias, token, dictionary, lexemes FROM ts_debug('public.english', 'The Brightest supernovaes'); alias | token | dictionary | lexemes -----------+-------------+----------------+------------- asciiword | The | english_ispell | {} blank | | | asciiword | Brightest | english_ispell | {bright} blank | | | asciiword | supernovaes | english_stem | {supernova}
12.8.2. Parser Testing
The following functions allow direct testing of a text search parser.
ts_parse(parser_name
text
,document
text
, OUTtokid
integer
, OUTtoken
text
) returnssetof record
ts_parse(parser_oid
oid
,document
text
, OUTtokid
integer
, OUTtoken
text
) returnssetof record
ts_parse
parses the given document
and returns a series of records, one for each token produced by parsing. Each record includes a tokid
showing the assigned token type and a token
which is the text of the token. For example:
SELECT * FROM ts_parse('default', '123 - a number'); tokid | token -------+-------- 22 | 123 12 | 12 | - 1 | a 12 | 1 | number
ts_token_type(parser_name
text
, OUTtokid
integer
, OUTalias
text
, OUTdescription
text
) returnssetof record
ts_token_type(parser_oid
oid
, OUTtokid
integer
, OUTalias
text
, OUTdescription
text
) returnssetof record
ts_token_type
returns a table which describes each type of token the specified parser can recognize. For each token type, the table gives the integer tokid
that the parser uses to label a token of that type, the alias
that names the token type in configuration commands, and a short description
. For example:
SELECT * FROM ts_token_type('default'); tokid | alias | description -------+-----------------+------------------------------------------ 1 | asciiword | Word, all ASCII 2 | word | Word, all letters 3 | numword | Word, letters and digits 4 | email | Email address 5 | url | URL 6 | host | Host 7 | sfloat | Scientific notation 8 | version | Version number 9 | hword_numpart | Hyphenated word part, letters and digits 10 | hword_part | Hyphenated word part, all letters 11 | hword_asciipart | Hyphenated word part, all ASCII 12 | blank | Space symbols 13 | tag | XML tag 14 | protocol | Protocol head 15 | numhword | Hyphenated word, letters and digits 16 | asciihword | Hyphenated word, all ASCII 17 | hword | Hyphenated word, all letters 18 | url_path | URL path 19 | file | File or path name 20 | float | Decimal notation 21 | int | Signed integer 22 | uint | Unsigned integer 23 | entity | XML entity
12.8.3. Dictionary Testing
The ts_lexize
function facilitates dictionary testing.
ts_lexize(dict
regdictionary
,token
text
) returnstext[]
ts_lexize
returns an array of lexemes if the input token
is known to the dictionary, or an empty array if the token is known to the dictionary but it is a stop word, or NULL
if it is an unknown word.
Examples:
SELECT ts_lexize('english_stem', 'stars'); ts_lexize ----------- {star} SELECT ts_lexize('english_stem', 'a'); ts_lexize ----------- {}
Note
The ts_lexize
function expects a single token, not text. Here is a case where this can be confusing:
SELECT ts_lexize('thesaurus_astro', 'supernovae stars') is null; ?column? ---------- t
The thesaurus dictionary thesaurus_astro
does know the phrase supernovae stars
, but ts_lexize
fails since it does not parse the input text but treats it as a single token. Use plainto_tsquery
or to_tsvector
to test thesaurus dictionaries, for example:
SELECT plainto_tsquery('supernovae stars'); plainto_tsquery ----------------- 'sn'