The Information Schema INNODB_FT_INDEX_CACHE table contains information about rows that have recently been inserted into an InnoDB fulltext index. To avoid re-organizing the fulltext index each time a change is made, which would be very expensive, new changes are stored separately and only integrated when an OPTIMIZE TABLE is run.

The SUPER privilege is required to view the table, and it also requires the innodb_ft_aux_table system variable to be set.

It has the following columns:

Note that for OPTIMIZE TABLE to process InnoDB fulltext index data, the innodb_optimize_fulltext_only system variable needs to be set to 1. When this is done, and an OPTIMIZE TABLE statement run, the INNODB_FT_INDEX_CACHE table will be emptied, and the INNODB_FT_INDEX_TABLE table will be updated.

Examples

SELECT * FROM INNODB_FT_INDEX_CACHE;
+------------+--------------+-------------+-----------+--------+----------+
| WORD       | FIRST_DOC_ID | LAST_DOC_ID | DOC_COUNT | DOC_ID | POSITION |
+------------+--------------+-------------+-----------+--------+----------+
| and        |            4 |           4 |         1 |      4 |        0 |
| arrived    |            4 |           4 |         1 |      4 |       20 |
| ate        |            1 |           1 |         1 |      1 |        4 |
| everybody  |            1 |           1 |         1 |      1 |        8 |
| goldilocks |            4 |           4 |         1 |      4 |        9 |
| hungry     |            3 |           3 |         1 |      3 |        8 |
| then       |            4 |           4 |         1 |      4 |        4 |
| wicked     |            2 |           2 |         1 |      2 |        4 |
| witch      |            2 |           2 |         1 |      2 |       11 |
+------------+--------------+-------------+-----------+--------+----------+
9 rows in set (0.00 sec)

INSERT INTO test.ft_innodb VALUES(3,'And she ate a pear');

SELECT * FROM INNODB_FT_INDEX_CACHE;
+------------+--------------+-------------+-----------+--------+----------+
| WORD       | FIRST_DOC_ID | LAST_DOC_ID | DOC_COUNT | DOC_ID | POSITION |
+------------+--------------+-------------+-----------+--------+----------+
| and        |            4 |           5 |         2 |      4 |        0 |
| and        |            4 |           5 |         2 |      5 |        0 |
| arrived    |            4 |           4 |         1 |      4 |       20 |
| ate        |            1 |           5 |         2 |      1 |        4 |
| ate        |            1 |           5 |         2 |      5 |        8 |
| everybody  |            1 |           1 |         1 |      1 |        8 |
| goldilocks |            4 |           4 |         1 |      4 |        9 |
| hungry     |            3 |           3 |         1 |      3 |        8 |
| pear       |            5 |           5 |         1 |      5 |       14 |
| she        |            5 |           5 |         1 |      5 |        4 |
| then       |            4 |           4 |         1 |      4 |        4 |
| wicked     |            2 |           2 |         1 |      2 |        4 |
| witch      |            2 |           2 |         1 |      2 |       11 |
+------------+--------------+-------------+-----------+--------+----------+

OPTIMIZE TABLE test.ft_innodb\G
*************************** 1. row ***************************
   Table: test.ft_innodb
      Op: optimize
Msg_type: note
Msg_text: Table does not support optimize, doing recreate + analyze instead
*************************** 2. row ***************************
   Table: test.ft_innodb
      Op: optimize
Msg_type: status
Msg_text: OK
2 rows in set (2.24 sec)

SELECT * FROM INNODB_FT_INDEX_CACHE;
+------------+--------------+-------------+-----------+--------+----------+
| WORD       | FIRST_DOC_ID | LAST_DOC_ID | DOC_COUNT | DOC_ID | POSITION |
+------------+--------------+-------------+-----------+--------+----------+
| and        |            4 |           5 |         2 |      4 |        0 |
| and        |            4 |           5 |         2 |      5 |        0 |
| arrived    |            4 |           4 |         1 |      4 |       20 |
| ate        |            1 |           5 |         2 |      1 |        4 |
| ate        |            1 |           5 |         2 |      5 |        8 |
| everybody  |            1 |           1 |         1 |      1 |        8 |
| goldilocks |            4 |           4 |         1 |      4 |        9 |
| hungry     |            3 |           3 |         1 |      3 |        8 |
| pear       |            5 |           5 |         1 |      5 |       14 |
| she        |            5 |           5 |         1 |      5 |        4 |
| then       |            4 |           4 |         1 |      4 |        4 |
| wicked     |            2 |           2 |         1 |      2 |        4 |
| witch      |            2 |           2 |         1 |      2 |       11 |
+------------+--------------+-------------+-----------+--------+----------+
13 rows in set (0.00 sec)

The OPTIMIZE TABLE statement has no effect, because the innodb_optimize_fulltext_only variable wasn't set:

SHOW VARIABLES LIKE 'innodb_optimize_fulltext_only';
+-------------------------------+-------+
| Variable_name                 | Value |
+-------------------------------+-------+
| innodb_optimize_fulltext_only | OFF   |
+-------------------------------+-------+

SET GLOBAL innodb_optimize_fulltext_only =1;

OPTIMIZE TABLE test.ft_innodb;
+----------------+----------+----------+----------+
| Table          | Op       | Msg_type | Msg_text |
+----------------+----------+----------+----------+
| test.ft_innodb | optimize | status   | OK       |
+----------------+----------+----------+----------+

SELECT * FROM INNODB_FT_INDEX_CACHE;
Empty set (0.00 sec)