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Post date: Nov 08, 2012 7:50:49 PM
For each slice of the query plan there is at least one query executor worker process assigned. During query execution, each segment will have a number of processes working on the query in parallel. Related processes that are working on the same portion of the query plan on different segments are referred to as gangs.
resource_cleanup_gangs_on_wait - Server parameter Cleans up idle segment worker processes before taking a slot in the resource queue.
Understanding Parallel Query Execution
Greenplum creates a number of database processes to handle the work of a query. On the master, the query worker process is called the query dispatcher (QD). The QD is responsible for creating and dispatching the query plan, and for accumulating and presenting the final results. On the segments, a query worker process is called a query executor (QE). A QE is responsible for completing its portion of work and communicating its intermediate results to the other worker processes.
For each slice of the query plan there is at least one worker process assigned. A worker process works on its assigned portion of the query plan independently. During query execution, each segment will have a number of processes working on the query in parallel.
Related processes that are working on the same portion of the query plan are referred to as gangs. As a portion of work is completed, tuples flow up the query plan from one gang of processes to the next. This inter-process communication between the segments is what is referred to as the interconnect component of Greenplum Database.