A new dynamic thread assignment (DTA) model enhances the use of worker threads.
Version 15.7 SP100 introduced a feature to generate a graphical query plan in HTML format for viewing data in a Web browser using the static thread assignment (STA) worker thread model. Using STA, there is a direct relationship between plan fragments and worker threads: as many plan fragments are generated as there are worker threads assigned to execute the query. The assignment of plan fragments to worker threads is static and unique: a worker thread can only execute the plan fragment assigned. Using this model, the HTML representation prints each thread with the details about its single plan fragment execution.
In version 16.0, the DTA worker thread model has been implemented. With the introduction of DTA, the Query Plan and Execution Statistics in HTML feature has been updated to correctly reflect the new parallel execution model. See Query Performance Improvements for more information about the DTA worker thread model.
The HTML representation reports the execution statistics per plan fragment execution (or work units), allowing several executions of the same plan fragment to be reported separately. To better identify the work unit execution following the new DTA model, for each plan fragment execution, the output is indicated by "Work unit execution" and provides the SPID for the thread and additional values such as the Root operator identifier (for the plan fragment) and producer ID.
This is an example of a query executed in parallel using several worker threads.
