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Manual:searchindex table


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Manual:Contents MediaWiki database layout searchindex table


The searchindex table is used to provide full text searches . Before MySQL 5.6, full text indexes were only provided by the MyISAM table engine, but not by InnoDB. The text table (cur table in 1.4 and earlier) however uses the InnoDB type to improve concurrency, so a copy of the current page text was required in order to make use of these indexes. This is the reason why this table is there. If using Postgres, this table does not exist: the full text information is stored as columns in the page and pagecontent tables directly.

FieldsEdit

si_pageEdit

Key to page_id .

si_titleEdit

Munged version of page title.

si_textEdit

Munged version of the current text of the page.

DetailsEdit

Indexes for this, using en wikipedia for cardinality:

+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table       | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| searchindex |          0 | si_page  |            1 | si_page     | A         |      797275 |     NULL | NULL   |      | BTREE      |         |
| searchindex |          1 | si_title |            1 | si_title    | A         |      265758 |     NULL | NULL   |      | FULLTEXT   |         |
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+

A common search query is of the form:

SELECT page_id, page_namespace, page_title FROM `page`,`searchindex`
WHERE page_id=si_page
AND MATCH(si_text) AGAINST('+''searchterm''' IN BOOLEAN MODE)
AND page_is_redirect=0
AND page_namespace IN (0)
LIMIT 20

In MediaWiki version 1.4 and earlier:

SELECT cur_id,cur_namespace,cur_title,cur_text FROM cur,searchindex
WHERE cur_id=si_page
AND (
  MATCH(si_text) AGAINST('+''searchterm''' IN BOOLEAN MODE)
  AND cur_is_redirect=0
)
AND cur_namespace IN (0,9,11)
LIMIT 0, 20;

Explain shows the following:

+-------------+--------+-------------------------------------------+---------------+---------+------------+--------+-------------+
| table       | type   | possible_keys                             | key           | key_len | ref        | rows   | Extra       |
+-------------+--------+-------------------------------------------+---------------+---------+------------+--------+-------------+
| cur         | range  | cur_id,cur_namespace,name_title_timestamp | cur_namespace |       1 | NULL       | 317499 | Using where |
| searchindex | eq_ref | si_page                                   | si_page       |       4 | cur.cur_id |      1 | Using where |
+-------------+--------+-------------------------------------------+---------------+---------+------------+--------+-------------+

Known problemsEdit

A range scan with namespaces containing a large number of records requires that a large portion of the searchindex table be loaded into RAM. This is very costly, in part because the searchindex table contains the full text of the article. A long term plan is to remove the text from the searchindex table. Temporary measures may involve adding fields to searchindex and indexing them (and using a self join to allow both that index and the fulltext index to be used) or adding a searchindex index to decrease the number of complete searchindex records which must be read to match the query.

Schema summaryEdit

MediaWiki version: 1.10

DESCRIBE searchindex;

+----------+------------------+------+-----+---------+-------+
| Field    | Type             | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+-------+
| si_page  | int(10) unsigned | NO   | PRI | NULL    |       |
| si_title | varchar(255)     | NO   | MUL |         |       |
| si_text  | mediumtext       | NO   | MUL | NULL    |       |
+----------+------------------+------+-----+---------+-------+
MediaWiki versions: 1.1 – 1.9

DESCRIBE searchindex;

+----------+-----------------+------+-----+---------+-------+
| Field    | Type            | Null | Key | Default | Extra |
+----------+-----------------+------+-----+---------+-------+
| si_page  | int(8) unsigned | NO   | PRI | NULL    |       |
| si_title | varchar(255)    | NO   | MUL | NULL    |       |
| si_text  | mediumtext      | NO   | MUL | NULL    |       |
+----------+-----------------+------+-----+---------+-------+