Manual:Querycache table

The querycache table is used for caching expensive grouped queries. This table is populated with the  maintenance script.

qc_type
A key name, generally the base name of the special page.

qc_value
Some sort of stored value. Sizes, counts...

qc_namespace
Target namespace. Used in conjunction with qc_title.

qc_title
Target title. Used in conjunction with qc_namespace.

Schema summary
+--+--+--+-+-+---+ +--+--+--+-+-+---+ +--+--+--+-+-+---+
 * Field       | Type             | Null | Key | Default | Extra |
 * qc_type     | varbinary(32)    | NO   | MUL | NULL    |       |
 * qc_value    | int(10) unsigned | NO   |     | 0       |       |
 * qc_namespace | int(11)         | NO   |     | 0       |       |
 * qc_title    | varbinary(255)   | NO   |     |         |       |

+--+-+--+-+-+---+ +--+-+--+-+-+---+ +--+-+--+-+-+---+
 * Field       | Type                | Null | Key | Default | Extra |
 * qc_type     | varbinary(32)       | NO   | MUL | NULL    |       |
 * qc_value    | int(10) unsigned    | NO   |     | 0       |       |
 * qc_namespace | int(11)            | NO   |     | 0       |       |
 * qc_title    | char(255) binary    | NO   |     | NULL    |       |

+--+-+--+-+-+---+ +--+-+--+-+-+---+ +--+-+--+-+-+---+
 * Field       | Type                | Null | Key | Default | Extra |
 * qc_type     | char(32)            | NO   | MUL | NULL    |       |
 * qc_value    | int(5) unsigned     | NO   |     | 0       |       |
 * qc_namespace | int(11)            | NO   |     | 0       |       |
 * qc_title    | char(255) binary    | NO   |     | NULL    |       |

+--+-+--+-+-+---+ +--+-+--+-+-+---+ +--+-+--+-+-+---+
 * Field       | Type                | Null | Key | Default | Extra |
 * qc_type     | char(32)            | NO   | MUL | NULL    |       |
 * qc_value    | int(5) unsigned     | NO   |     | 0       |       |
 * qc_namespace | tinyint(2) unsigned | NO  |     | 0       |       |
 * qc_title    | char(255) binary    | NO   |     | NULL    |       |

Indexes
 +++--+--+-+---+-+--++--++-+---+ +++--+--+-+---+-+--++--++-+---+ +++--+--+-+---+-+--++--++-+---+
 * Table     | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
 * querycache |         1 | qc_type  |            1 | qc_type     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
 * querycache |         1 | qc_type  |            2 | qc_value    | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |