1. Were the keys composite or not? The correct key for the queries you listed is (device_id, date_added DESC). In MySQL you'd add this by doing "ALTER TABLE l

1. Were the keys composite or not? The correct key for the queries you listed is (device_id, date_added DESC). In MySQL you'd add this by doing "ALTER TABLE location ADD INDEX (device_id, date_added DESC)" MySQL uses one key per query, so having an index on (device_id) and an index on (date_added) individually will do no (or very little) good for the queries you listed. 2. MyISAM uses table-level locking. This will block all reads (selects) while writes (insert, update, delete) are happening. It does not prevent multiple selects from happening at the same time. If you have a write-heavy table that you are also reading from you need to be using InnoDB. 3. SELECT COUNT(*) FROM location should be instantaneous in MyISAM . It will be slow(er) in InnoDB. If this query was blocking it's because something was trying to write to the table. 4. Foreign key constraints have nothing to do with anything here. That's one advantage of InnoDB, although most web apps I know don't use them, but not one that would help you. Rather, what will help you is the table-level vs. row-level for MyISAM vs. InnoDB. This allows selects to happen to unaffected rows while writes are happening.