Maximum Slots in a Plex and performance

A slot roughly corresponds to a thread and the maximum number of threads-per-process for a JCC on Linux is 4096, so this maximum is intended to prevent an overload where too many threads are created.

A snap consumes one slot as long as it is running, so it will be freed up as soon as it finishes. Presumably, you are not running 1,900 child executions simultaneously, so you are probably not going to reach the limit. Are you executing all child pipelines locally (i.e. the Snaplex setting in PipelineExecute is blank) or are spreading executions across other nodes in the Snaplex?

In the Dashboard, you can view the active thread count by going to a node, clicking the dropdown arrow and selecting the ‘Additional Information’ menu item. That should open a dialog with some more stats, in particular check the “Active Threads” count to see how high it is. If it really is close to 4,000 then it might be a bottleneck.
You can also check the parent executions to see if there any status messages on the Pipeline Execute snap, it will indicate if it has to wait for resources to become available. Note that you will need to bump up the limits for the JCC process before you can safely increase the Max Slots in the Snaplex settings.

In general, if you’re looking for bottlenecks in your pipeline executions, look at the “Duration” column in the execution statistics window. In particular, look for long blue bars which indicate that the snap is actively working on something (see the Check Pipeline Execution Statistics documentation for more information).