Sys Queue

The MonetDB kernel maintains an active queue of all running queries. This queue is available for all users to inspect the status of his own queries. The system administrator can inspect it to overlook the complete workload on the system. The queue is made visible as a table producing function sys.queue().

The schema structure is largely self-explanatory. If the query (template) is ran multiple times, then the system can derive a progress indicator and calculate an estimated time of completion. The 'tag' column references the query log tables, provided this facility has been turned on. The initial column 'qtag' provides a key to each active query .

One can use the SQL procedures PAUSE, RESUME and STOP to control the execution of (long) running queries.

NOTE that PAUSE and STOP takes effect at the first safe point within the query plan, which often is after the current MAL instruction has been finished. For complex queries over large database this may take seconds up to minutes.