Unexplained InnoDB timeouts

I've been seeing some very basic updates timing out lately and have not been able to determine the cause. An example:

//# Query_time: 51 Lock_time: 0 Rows_sent: 0 Rows_examined: 0

UPDATE photos SET position = position + 1 WHERE (photo_album_id = 40470);

The same log has no entries with a Lock_time > 0. Running show innodb status does not reveal any related locks either. This problem appears to be affecting at least 5 different tables based on my app server logs (which show a Mysql::Error: Lock wait timeout exceeded error related to each corresponding entry in the mysql-slow log).

Any idea on where to go from here? I'm hitting dead-ends in all directions. Thanks.

EDIT:

CREATE TABLE photos (
id int(11) NOT NULL auto_increment,
type varchar(255) NOT NULL,
photo_album_id int(11) NOT NULL,
user_id int(11) NOT NULL,
title varchar(255) default 'Untitled',
description text,
credit varchar(255) default NULL,
photo_file_name varchar(255) default NULL,
photo_content_type varchar(255) default NULL,
photo_file_size int(11) default NULL,
photo_updated_at datetime default NULL,
position int(11) default '0',
views int(11) default '0',
folder varchar(255) default NULL,
published tinyint(1) default '0',
published_at datetime default NULL,
created_at datetime default NULL,
updated_at datetime default NULL,
album_published tinyint(1) default '0',
comment_count int(11) default '0',
audio_file_name varchar(255) default NULL,
audio_content_type varchar(255) default NULL,
audio_file_size int(11) default NULL,
audio_updated_at datetime default NULL,
cover tinyint(1) default '0',
slug varchar(255) default NULL,
comments_count int(11) default '0',
delete_from_s3 tinyint(1) default '0',
batch int(11) default NULL,
audio varchar(255) default NULL,
PRIMARY KEY (id),
KEY index_photos_on_album_published (album_published),
KEY index_photos_on_batch

I know this is really late, but you really need to capture the output of SHOW ENGINE INNODB STATUS; during that query to see why it's waiting.

If it happens a lot during a specific time, it would be easy to just grab that output every x seconds and hope you capture it (or perhaps artificially generate the load).

StackExchange Database Administrators Q#928, answer score: 3