How to compact the Monitor database in a Red Hat Ceph Storage cluster?

Issue

1. How to compact the MON store db in a Red Hat Ceph Storage cluster?

• The monitor logs as well as ceph -s shows the following message:

mon.ceph1 store is getting too big! 48031 MB >= 15360 MB -- 62% avail
mon.ceph2 store is getting too big! 47424 MB >= 15360 MB -- 63% avail
mon.ceph3 store is getting too big! 46524 MB >= 15360 MB -- 63% avail

• The monitor database seems to be large in size:

# du -sch /var/lib/ceph/mon/ceph-ceph1/store.db/
47G     /var/lib/ceph/mon/ceph-ceph1/store.db/
47G     total

2. The MON database size seems to increase even if the process was restarted after setting mon_compact_on_start = true in ceph.conf, why?