About threads, watchers, poling and licenses

Number of threads that qualify for license count is sum of nProcThreads and nProcThreadsHigh (on the user interface they're called "Number of processing threads at normal priority" and "Number of processing threads at high priority": see Service configuration for details).

The sum of two must non exceed the number of threads specified in the Back4 license otherwise an error message is displayed and Back4 won't start or will stop process items.

Number of polling threads (nPollingThreads) are not counted for licenses.

Polling threads are processes that, in regular intervals, poll the items to be monitored, e.g. email, feeds, workflows, Exalead indexing, cleanup etc. When a polling thread finds something changes, it creates a scheduled task in the database.

DBPoller is a special one that loads the scheduled tasks in the memory and passes them to Back4 for executing.

How much polling threads you need?

The default value is 1, and that means that all polling process will queue one after each other. Should you set 10 polling threads, you don't have to feat e performance degradation.

If the polling points to a folder on a server different of that where Back4 runs, when you reboot that server, the poling will be interrupted. Restart Back4 service to reestablish the normal operations.

Every queue has an internal and automatic watchers that identify a newly arrived file and create a scheduled task to be processed by Back4.

Watchers are not counted for licenses.

This depends on:

•The number of processes

•The number of of items every process needs to elaborate

•The time required to elaborate an item.

Even should you have only one process (it's absolutely unrealistic, but let's take it for an example), you may need more than one thread. Let's assume that you have one thread, and one queue that receive one image every 10 seconds, and that the average processing time for each image is about 20 seconds. This means your image queue will continue to grow because images will arrive faster then being processed. You need at least two threads to work in parallel - each will take one image and process it in 20 seconds, just in time for new images to arrive and to start being processed.

Why not set up 1000 threads? Because each thread requires memory and CPU ticks, and your Back4 hardware has not unlimited power.

You may expect for a well sized Back4 server to have CPU all the time on about 80%, but not more, and never on 100%. Should the CPU usage be more of that, you have too many threads for the given hardware - either reduce threads, or add a new Back4 server (pointing to the same GN4 database.