On 1/6/2011 7:53 AM, Matt Pouttu-Clarke wrote:
Multi-thread access to read-only DB in embedded mode? Hi All,

I am using Derby as an embedded database within a Hadoop job to lookup IP geographic info.  
http://mpouttuclarke.wordpress.com/2010/12/10/java-embedded-db-for-ip2location-in-hadoop/

The problem is that Hadoop has an option called JVM sharing where more than one thread may be active in the JVM instance.  Since the embedded option only supports one thread at a time, I have had to turn off JVM sharing for my IP lookup job (by setting mapred.job.reuse.jvm.num.tasks to 1).

Embedded definitely supports more than one thread at a time as long as all of those threads are in the same JVM.  Each thread should just have it's own separate  Connection.