Do MySQL Locked Tables affect related Views?

Question

So after reading Performance in PDO / PHP / MySQL: transaction versus direct execution in regards to performance issues I was thinking about I did some research on locking tables in MySQL.

On http://dev.mysql.com/doc/refman/5.0/en/table-locking.html

Table locking enables many sessions to read from a table at the same time, but if a session wants to write to a table, it must first get exclusive access. During the update, all other sessions that want to access this particular table must wait until the update is done.

This part struck me particularly because most of our queries will be updates rather than inserts. I was wondering if one created a table called foo on which all updates/inserts were carried out and then a view called foo_view (A copy of foo, or perhaps foo and a linkage of several other tables plus foo) on which all selects occurred, would this locking issue still occur?

That is, would SELECT queries on foo_view still have to wait for an update to finish on foo?

Another brief question my colleague asked. Does this affect caching? I.e. if the SELECT is cached will it hit the cache and return results, or will it wait for the lock to finish first?

Answer 1

Your view will experience the same locking as the underlying tables.

From the MySQL Reference page on locking:

MySQL grants table write locks as follows:

1. If there are no locks on the table, put a write lock on it.
2. Otherwise, put the lock request in the write lock queue.

MySQL grants table read locks as follows:

1. If there are no write locks on the table, put a read lock on it.
2. Otherwise, put the lock request in the read lock queue.

It's worth mentioning that this depends on the database engine you are using. MyISAM will follow the steps above and lock the entire table (even if it is split into multiple partitions) where an engine like InnoDB will do row level locking instead.

If you're not reaching the necessary performance benchmarks with MyISAM and you have shown your bottleneck is waiting on table locks via updates, I would suggest changing the storage engine of your table to InnoDB.