# Allowed engines

You can specify the number of TERR engines that can run concurrently, and the number of TERR engines that are allocated in the TERR service queue.

Configuration property | Default setting | Description
--- | --- | ---
`engine.session.max` | <one less than the number of logical processors available on the node> | The maximum number of TERR engine sessions that are allowed to run concurrently in the TERR service. Each user running data functions in a Spotfire analysis uses its own session. The default is one less than the number of logical processors on the host.
`engine.queue.size` | <one quarter of the number of logical processors on the host, constrained to a minimum of 1 and a maximum of 10. > | The number of TERR engines preallocated and available for new sessions in the TERR service queue. The service always starts enough engines to keep the queue at the requested level. The total number of engines that can run at the same time is the sum of `engine.session.max` + `engine.queue.size`. This number can be set manually to a value higher than 10.

For more information on how engine resources can be managed, see Service resource management scenarios.