If you activate extended Logging, the lookup-function in the change-log tab fails on large databases.

The following query causes the problem:

"SELECT DISTINCT lt.id FROM `civicrm`.`log_civicrm_note` lt
WHERE lt.log_conn_id = 219
AND lt.log_date BETWEEN DATE_SUB('20140424093302', INTERVAL 10 SECOND)
AND DATE_ADD('20140424093302', INTERVAL 10 SECOND)
AND ( entity_id = 202 AND entity_table = 'civicrm_contact' )
OR (entity_id IN (SELECT note.id FROM `civicrm`.log_civicrm_note note
WHERE note.entity_id = 202 AND note.entity_table = 'civicrm_contact')
AND entity_table = 'civicrm_note');"

More precisely, the last part of the query:

"AND ( entity_id = 202 AND entity_table = 'civicrm_contact' )
OR (entity_id IN (SELECT note.id FROM `civicrm`.log_civicrm_note note
WHERE note.entity_id = 202 AND note.entity_table = 'civicrm_contact')
AND entity_table = 'civicrm_note');"

(built by CRM/Logging/Differ.php:79 as $contactIdClause) should
obviously filter the notes associated to a specific contact.
But the lack of parenthesis around the OR-operator changes the hierarchy
of the entire WHERE clause.

I think this should be one AND-clause with an encapsulated OR-clause:

"AND (( entity_id = 202 AND entity_table = 'civicrm_contact' ) OR
(entity_id IN (SELECT note.id FROM `civicrm`.log_civicrm_note note WHERE
note.entity_id = 202 AND note.entity_table = 'civicrm_contact') AND
entity_table = 'civicrm_note'));"