Ceph

OSD heartbeat timeout due to too many omap entries read in each 'chunk' being backfilled

Version-Release number of selected component (if applicable):
jewel

How reproducible:
Always in the RH scale lab

Additional info:

Testing in the scale lab uncovered an area where osds were
hitting heartbeat timeouts during backfill.

This turned out to be due to too many omap entries read in each 'chunk'
being backfilled, and only resetting the heartbeat once an entire chunk was assembled. We should ask users to tune this down for their
bucket index osds - setting:

Max number of omap entries per chunk:

osd_recovery_max_omap_entries_per_chunk = 1024

Josh is planning to add a patch for luminous and jewel to reset the heartbeat in middle of gathering a chunk, which should make the current default of 64000 entries per backfill chunk work even with large stores.