From: Stewart Smith Date: November 22 2011 12:52am Subject: Re: Concurrent table access from InnoDB List-Archive: http://lists.mysql.com/internals/38397 Message-Id: <877h2tnflg.fsf@flamingspork.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii On Mon, 21 Nov 2011 09:55:15 +0000, Mark Leith wrote: > This doesn't necessarily relate to the limitation of partitioned > tables not having a multi-threaded read of partitions under the > covers, as at the handler / SQL layer, MySQL is just waiting for the > storage engine to return rows to it at the current step of JOIN > execution - under the covers the storage engine could choose to access > the partitions of a single table concurrently if it wanted to (we just > don't have that in MySQL at the moment). NDB does this. Multiple data nodes may be sending data back to the MySQL server at once. This is a pretty limited form of parallelism though. Basically, concurrent query execution is hard and for the vast majority of queries that MySQL processes, wouldn't see any or much improvement - avoiding the added complexity (and performance impact for non parallelized queries) of locking is a pretty big benefit. -- Stewart Smith