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Re: select distinct slower in 5.0 than 4.1
Posted by: Jay Pipes
Date: December 19, 2005 10:49AM

Saar Barhoom wrote:
> On 4.1.16 this query runs very fast. Using the
> EXPLAIN SELECT I see that the 'type' of the query
> is 'ref'.
> On 5.0.16 this query runs very slow (about x20
> times slower). EXPLAIN SELECT show that the 'type'
> of the query is 'range'.
>
> Could that be related to the loose index scan
> feature of 5.0?

Probably not; with the loose index scan, you'd see something like "Using index group-by" in the Extra column, if I remember correctly...

More likely, it might be a difference in the data setsbeing operated on. Are both schema identical? Are the data sets identical? Also, could you post the SHOW CREATE TABLE and EXPLAIN output for each? Thanks!

Jay Pipes
Community Relations Manager, North America, MySQL Inc.

Got Cluster? http://www.mysql.com/cluster
Personal: http://jpipes.com

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