June 9th, 2013 at 3:22 pm
One or more Query Plan Nodes for a single Query Plan that are executed together in the . Plan Fragments can be invoked at multiple partitions for each query request (if that query needs to access data at multiple partitions). For example, consider the query “SELECT COUNT(*) FROM FOO”. Since this query access the table FOO at multiple partitions, the Query Plan is split into two parts: (1) get the number of rows from FOO at this partition and (2) sum the counts from each individual partition into a single aggregate value. The first Plan Fragment is sent to all of the partitions in the cluster, who each produce a single output table. Once the results from each partition arrive, then the second Plan Fragment is invoked at the transaction’s Base Partition.