Make *id fields unsigned.
function tracker_update_8001() {
db_drop_primary_key('tracker_user');
db_drop_index('tracker_user', 'tracker');
db_change_field('tracker_user', 'uid', 'uid', array(
'description' => 'The {users}.uid of the node author or commenter.',
'type' => 'int',
'unsigned' => TRUE,
'not null' => TRUE,
'default' => 0,
), array(
'primary key' => array(
'nid',
'uid',
),
'indexes' => array(
'tracker' => array(
'uid',
'published',
'changed',
),
),
));
}