Work queues

A work queue comprises the following components.

Work queue	A work queue is a database table that holds work items for processing. Guidewire work queues share the standard work item table: StandardWorkQueue (`pc_standardworkqueue`).
Writer	A writer thread does the following: It selects units of work for processing. It writes the identities of the work items to a work queue table. It notifies the workers that there are work items to process.
Worker	A worker retrieves or more work items from the work queue and processes the work items to completion. A worker only processes work items from its associated writer. By default, each work queue starts a single worker on each cluster member with the `workqueue` role, unless configured otherwise.
Executor	The work queue executor manages the worker tasks on each application server in a PolicyCenter cluster. If a work queue has no more remaining items to process, the executor shuts down all worker on a server node except for one, which periodically checks to see if there is new work to perform.

Starting the writer initiates a run of processing on a work queue. The work is complete if the workers exhaust the queue of all work items, except those that they failed to process successfully.