root@ceph-01:~# ceph config help rgw_dynamic_resharding
rgw_dynamic_resharding - Enable dynamic resharding
  (bool, basic)
  Default: true
  Can update at runtime: true
  Services: [rgw]
  See also: [rgw_max_objs_per_shard]

If true, RGW will dynamicall increase the number of shards in buckets that have a high number of objects per shard.
root@ceph-01:~# ceph daemon /var/run/ceph/ceph-client.rgw.ceph-01.59729.57693280.asok config get rgw_dynamic_resharding
{
    "rgw_dynamic_resharding": "true"
}
root@ceph-01:~# ceph config set client.rgw.ceph-01 rgw_dynamic_resharding false
root@ceph-01:~# ceph daemon /var/run/ceph/ceph-client.rgw.ceph-01.59729.57693280.asok config get rgw_dynamic_resharding
{
    "rgw_dynamic_resharding": "false"
}