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From Pavel Bortnovskiy <PBortnovs...@Jefferies.com>
Subject Fw: Left-Join extremely slow in comparison to Inner-Join. How to tune Derby?
Date Wed, 05 Jan 2011 17:16:16 GMT
In addition, what seems to be odd is that fetching the data takes most of 
the time from the total time.
For example (snapshot from Aqua Data Studio retrieving the data from the 
Derby in-memory table):



Would it be considered normal to take over 2 minutes to fetch 2,357 
records?

Here is the same snapshot when the Left-Join was converted to the 
Inner-Join:






----- Forwarded by Pavel Bortnovskiy/JEFCO on 01/05/2011 12:12 PM -----

From:
Pavel Bortnovskiy/JEFCO
To:
"Derby Discussion" <derby-user@db.apache.org>
Date:
01/05/2011 12:04 PM
Subject:
Left-Join extremely slow in comparison to Inner-Join. How to tune Derby?


Hello, all:

I am using Derby as an in-memory DB. While executing a complex query 
(which contains a union and several left-joins), we discovered that this 
query with a left join would take about 3.5 mins to execute and fetch the 
data, whereas the same query with the left join replaced with the inner 
join would take just 30 seconds.

What tools or API is available at our disposal to tune the in-memory 
Derby, to see its execution plan, to try to figure out why it is taking 
such an extraordinary time to fetch about 2,500-3000 records.

I also noticed that by running the same query over and over, the time to 
execute and fetch seems to be slowly creeping up as well - it started with 
2.5 mins, then grew to 3 mins and now it's almost 4 mins.

Any help would be greatly appreciated!

Regards,

Pavel.




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