Re: Concurrent table access from InnoDB

On Mon, 21 Nov 2011 09:55:15 +0000, Mark Leith <[email protected]> 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

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