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From Pavel Bortnovskiy <PBortnovs...@Jefferies.com>
Subject Left-Join extremely slow in comparison to Inner-Join. How to tune Derby?
Date Wed, 05 Jan 2011 17:04:32 GMT
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!



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