TempStatsStore derby.log

[Raj Hadoop]

Hi,
 
I have Hive metastore created in an Oracle database. 
 
But when i execute my Hive queries , I see following directory and file created.
TempStatsStore  (directory)
derby.log
 
What are this? Can one one suggest why derby log is created even though my 
javax.jdo.option.ConnectionURL is pointing to Oracle?
 
Thanks,
Raj