From MediaWiki.org
Objectcache table is used for a few generic cache operations if not using Memcached.
describe objectcache;
+---------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------------+------+-----+---------+-------+
| keyname | varchar(255) binary | | PRI | | |
| value | mediumblob | YES | | NULL | |
| exptime | datetime | YES | MUL | NULL | |
+---------+---------------------+------+-----+---------+-------+
DESCRIBE objectcache; in MediaWiki 1.8 gives the following:
+---------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+------------+------+-----+---------+-------+
| keyname | char(255) | NO | PRI | NULL | |
| value | mediumblob | YES | | NULL | |
| exptime | datetime | YES | MUL | NULL | |
+---------+------------+------+-----+---------+-------+
+---------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+------------+------+-----+---------+-------+
| keyname | char(255) | NO | PRI | NULL | |
| value | mediumblob | YES | | NULL | |
| exptime | datetime | YES | MUL | NULL | |
+---------+------------+------+-----+---------+-------+
+---------+-----------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-----------------+------+-----+---------+-------+
| keyname | varbinary(255) | NO | PRI | NULL | |
| value | mediumblob | YES | | NULL | |
| exptime | datetime | YES | MUL | NULL | |
+---------+-----------------+------+-----+---------+-------+
+---------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+------------+------+-----+---------+-------+
| keyname | char(255) | NO | PRI | NULL | |
| value | mediumblob | YES | | NULL | |
| exptime | datetime | YES | MUL | NULL | |
+---------+------------+------+-----+---------+-------+