mirror of
https://github.com/ceph/ceph
synced 2024-12-24 20:33:27 +00:00
57 lines
2.5 KiB
ReStructuredText
57 lines
2.5 KiB
ReStructuredText
==========
|
|
PG Removal
|
|
==========
|
|
|
|
See OSD::_remove_pg, OSD::RemoveWQ
|
|
|
|
There are two ways for a pg to be removed from an OSD:
|
|
|
|
1. MOSDPGRemove from the primary
|
|
2. OSD::advance_map finds that the pool has been removed
|
|
|
|
In either case, our general strategy for removing the pg is to
|
|
atomically set the metadata objects (pg->log_oid, pg->biginfo_oid) to
|
|
backfill and asynronously remove the pg collections. We do not do
|
|
this inline because scanning the collections to remove the objects is
|
|
an expensive operation.
|
|
|
|
OSDService::deleting_pgs tracks all pgs in the process of being
|
|
deleted. Each DeletingState object in deleting_pgs lives while at
|
|
least one reference to it remains. Each item in RemoveWQ carries a
|
|
reference to the DeletingState for the relevant pg such that
|
|
deleting_pgs.lookup(pgid) will return a null ref only if there are no
|
|
collections currently being deleted for that pg.
|
|
|
|
The DeletingState for a pg also carries information about the status
|
|
of the current deletion and allows the deletion to be cancelled.
|
|
The possible states are:
|
|
|
|
1. QUEUED: the PG is in the RemoveWQ
|
|
2. CLEARING_DIR: the PG's contents are being removed synchronously
|
|
3. DELETING_DIR: the PG's directories and metadata being queued for removal
|
|
4. DELETED_DIR: the final removal transaction has been queued
|
|
5. CANCELED: the deletion has been canceled
|
|
|
|
In 1 and 2, the deletion can be canceled. Each state transition
|
|
method (and check_canceled) returns false if deletion has been
|
|
canceled and true if the state transition was successful. Similarly,
|
|
try_stop_deletion() returns true if it succeeds in canceling the
|
|
deletion. Additionally, try_stop_deletion() in the event that it
|
|
fails to stop the deletion will not return until the final removal
|
|
transaction is queued. This ensures that any operations queued after
|
|
that point will be ordered after the pg deletion.
|
|
|
|
OSD::_create_lock_pg must handle two cases:
|
|
|
|
1. Either there is no DeletingStateRef for the pg, or it failed to cancel
|
|
2. We succeeded in canceling the deletion.
|
|
|
|
In case 1., we proceed as if there were no deletion occurring, except that
|
|
we avoid writing to the PG until the deletion finishes. In case 2., we
|
|
proceed as in case 1., except that we first mark the PG as backfilling.
|
|
|
|
Similarly, OSD::osr_registry ensures that the OpSequencers for those
|
|
pgs can be reused for a new pg if created before the old one is fully
|
|
removed, ensuring that operations on the new pg are sequenced properly
|
|
with respect to operations on the old one.
|