Javadoc
Overridden to use
BigdataSail#getReadOnlyConnection() as a
workaround to the test harness which invokes
BigdataSail#getConnection() multiple times from within the same
thread. When full transactions are not enabled, that will delegate to
BigdataSail#getUnisolatedConnection(). Only one unisolated
connection is permitted at a time. While different threads will block to
await the unisolated connection, that method will throw an exception if
there is an attempt by a single thread to obtain more than one instance
of the unisolated connection (since that operation would otherwise
deadlock).