[ceph-users] What is a pgmap?

I'm surprised I couldn't find this explained anywhere (I did look), but ... What is the pgmap and why does it get updated every few seconds on a tiny cluster that's mostly idle? I do know what a placement group (PG) is and that when documentation talks about placement group maps, it is talking about something else -- mapping of PGs to OSDs by CRUSH and OSD maps. -- Bryan Henderson San Jose, California