Data collection stopped, why?

You should probably open a support ticket as there is no specific valid reason to stop collecting. You may either have run out of space or started encountering an error (which could spin up extra processes and run out.) The ? just means you collected successfully at some time and have history but the latest collection didn't work.

Thanks, i did open a ticket, but thought this might be a quicker avenue. Do you use workload analysis to support production environments, or do you work for Idera? because here is another question. how come the PostGreSQL database grows explosively?

Yes, I do work for IDERA.

Support should be able to help you decide if the growth is unexpected. (Have you checked the space requirements in online help?)

It samples queries rapidly for correlation and there is no aggregation to reduce space usage yet. So it should grow until grooming kicks in at about a month. Support can help you adjust that period if you want. It is documented in online help as well.

Support also can provide a manual script to clear history if space is a concern.