28.4.18 The INFORMATION_SCHEMA INNODB_FT_INDEX_CACHE Table

The INNODB_FT_INDEX_CACHE table provides token information about newly inserted rows in a FULLTEXT index. To avoid expensive index reorganization during DML operations, the information about newly indexed words is stored separately, and combined with the main search index only when OPTIMIZE TABLE is run, when the server is shut down, or when the cache size exceeds a limit defined by the innodb_ft_cache_size or innodb_ft_total_cache_size system variable.

This table is empty initially. Before querying it, set the value of the innodb_ft_aux_table system variable to the name (including the database name) of the table that contains the FULLTEXT index (for example, test/articles).

For related usage information and examples, see Section 17.15.4, “InnoDB INFORMATION_SCHEMA FULLTEXT Index Tables”.

The INNODB_FT_INDEX_CACHE table has these columns:

• WORD

  A word extracted from the text of a newly inserted row.

• FIRST_DOC_ID

  The first document ID in which this word appears in the FULLTEXT index.

• LAST_DOC_ID

  The last document ID in which this word appears in the FULLTEXT index.

• DOC_COUNT

  The number of rows in which this word appears in the FULLTEXT index. The same word can occur several times within the cache table, once for each combination of DOC_ID and POSITION values.

• DOC_ID

  The document ID of the newly inserted row. This value might reflect the value of an ID column that you defined for the underlying table, or it can be a sequence value generated by InnoDB when the table contains no suitable column.

• POSITION

  The position of this particular instance of the word within the relevant document identified by the DOC_ID value. The value does not represent an absolute position; it is an offset added to the POSITION of the previous instance of that word.

Notes

• This table is empty initially. Before querying it, set the value of the innodb_ft_aux_table system variable to the name (including the database name) of the table that contains the FULLTEXT index (for example test/articles). The following example demonstrates how to use the innodb_ft_aux_table system variable to show information about a FULLTEXT index for a specified table.

  mysql> USE test;
  
  mysql> CREATE TABLE articles (
           id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
           title VARCHAR(200),
           body TEXT,
           FULLTEXT (title,body)
         ) ENGINE=InnoDB;
  
  mysql> INSERT INTO articles (title,body) VALUES
         ('MySQL Tutorial','DBMS stands for DataBase ...'),
         ('How To Use MySQL Well','After you went through a ...'),
         ('Optimizing MySQL','In this tutorial we show ...'),
         ('1001 MySQL Tricks','1. Never run mysqld as root. 2. ...'),
         ('MySQL vs. YourSQL','In the following database comparison ...'),
         ('MySQL Security','When configured properly, MySQL ...');
  
  mysql> SET GLOBAL innodb_ft_aux_table = 'test/articles';
  
  mysql> SELECT WORD, DOC_COUNT, DOC_ID, POSITION
         FROM INFORMATION_SCHEMA.INNODB_FT_INDEX_CACHE LIMIT 5;
  +------------+-----------+--------+----------+
  | WORD       | DOC_COUNT | DOC_ID | POSITION |
  +------------+-----------+--------+----------+
  | 1001       |         1 |      4 |        0 |
  | after      |         1 |      2 |       22 |
  | comparison |         1 |      5 |       44 |
  | configured |         1 |      6 |       20 |
  | database   |         2 |      1 |       31 |
  +------------+-----------+--------+----------+

• You must have the PROCESS privilege to query this table.

• Use the INFORMATION_SCHEMA COLUMNS table or the SHOW COLUMNS statement to view additional information about the columns of this table, including data types and default values.

• For more information about InnoDB FULLTEXT search, see Section 17.6.2.4, “InnoDB Full-Text Indexes”, and Section 14.9, “Full-Text Search Functions”.