mirror of https://github.com/ceph/ceph
132 lines
5.7 KiB
ReStructuredText
132 lines
5.7 KiB
ReStructuredText
===========================
|
|
Map and PG Message handling
|
|
===========================
|
|
|
|
Overview
|
|
--------
|
|
The OSD handles routing incoming messages to PGs, creating the PG if necessary
|
|
in some cases.
|
|
|
|
PG messages generally come in two varieties:
|
|
|
|
1. Peering Messages
|
|
2. Ops/SubOps
|
|
|
|
There are several ways in which a message might be dropped or delayed. It is
|
|
important that the message delaying does not result in a violation of certain
|
|
message ordering requirements on the way to the relevant PG handling logic:
|
|
|
|
1. Ops referring to the same object must not be reordered.
|
|
2. Peering messages must not be reordered.
|
|
3. Subops must not be reordered.
|
|
|
|
MOSDMap
|
|
-------
|
|
MOSDMap messages may come from either monitors or other OSDs. Upon receipt, the
|
|
OSD must perform several tasks:
|
|
|
|
1. Persist the new maps to the filestore.
|
|
Several PG operations rely on having access to maps dating back to the last
|
|
time the PG was clean.
|
|
2. Update and persist the superblock.
|
|
3. Update OSD state related to the current map.
|
|
4. Expose new maps to PG processes via *OSDService*.
|
|
5. Remove PGs due to pool removal.
|
|
6. Queue dummy events to trigger PG map catchup.
|
|
|
|
Each PG asynchronously catches up to the currently published map during
|
|
process_peering_events before processing the event. As a result, different
|
|
PGs may have different views as to the "current" map.
|
|
|
|
One consequence of this design is that messages containing submessages from
|
|
multiple PGs (MOSDPGInfo, MOSDPGQuery, MOSDPGNotify) must tag each submessage
|
|
with the PG's epoch as well as tagging the message as a whole with the OSD's
|
|
current published epoch.
|
|
|
|
MOSDPGOp/MOSDPGSubOp
|
|
--------------------
|
|
See OSD::dispatch_op, OSD::handle_op, OSD::handle_sub_op
|
|
|
|
MOSDPGOps are used by clients to initiate rados operations. MOSDSubOps are used
|
|
between OSDs to coordinate most non peering activities including replicating
|
|
MOSDPGOp operations.
|
|
|
|
OSD::require_same_or_newer map checks that the current OSDMap is at least
|
|
as new as the map epoch indicated on the message. If not, the message is
|
|
queued in OSD::waiting_for_osdmap via OSD::wait_for_new_map. Note, this
|
|
cannot violate the above conditions since any two messages will be queued
|
|
in order of receipt and if a message is received with epoch e0, a later message
|
|
from the same source must be at epoch at least e0. Note that two PGs from
|
|
the same OSD count for these purposes as different sources for single PG
|
|
messages. That is, messages from different PGs may be reordered.
|
|
|
|
|
|
MOSDPGOps follow the following process:
|
|
|
|
1. OSD::handle_op: validates permissions and crush mapping.
|
|
discard the request if they are not connected and the client cannot get the reply ( See OSD::op_is_discardable )
|
|
See OSDService::handle_misdirected_op
|
|
See PG::op_has_sufficient_caps
|
|
See OSD::require_same_or_newer_map
|
|
2. OSD::enqueue_op
|
|
|
|
MOSDSubOps follow the following process:
|
|
|
|
1. OSD::handle_sub_op checks that sender is an OSD
|
|
2. OSD::enqueue_op
|
|
|
|
OSD::enqueue_op calls PG::queue_op which checks waiting_for_map before calling OpWQ::queue which adds the op to the queue of the PG responsible for handling it.
|
|
|
|
OSD::dequeue_op is then eventually called, with a lock on the PG. At
|
|
this time, the op is passed to PG::do_request, which checks that:
|
|
|
|
1. the PG map is new enough (PG::must_delay_op)
|
|
2. the client requesting the op has enough permissions (PG::op_has_sufficient_caps)
|
|
3. the op is not to be discarded (PG::can_discard_{request,op,subop,scan,backfill})
|
|
4. the PG is active (PG::flushed boolean)
|
|
5. the op is a CEPH_MSG_OSD_OP and the PG is in PG_STATE_ACTIVE state and not in PG_STATE_REPLAY
|
|
|
|
If these conditions are not met, the op is either discarded or queued for later processing. If all conditions are met, the op is processed according to its type:
|
|
|
|
1. CEPH_MSG_OSD_OP is handled by PG::do_op
|
|
2. MSG_OSD_SUBOP is handled by PG::do_sub_op
|
|
3. MSG_OSD_SUBOPREPLY is handled by PG::do_sub_op_reply
|
|
4. MSG_OSD_PG_SCAN is handled by PG::do_scan
|
|
5. MSG_OSD_PG_BACKFILL is handled by PG::do_backfill
|
|
|
|
CEPH_MSG_OSD_OP processing
|
|
--------------------------
|
|
|
|
ReplicatedPG::do_op handles CEPH_MSG_OSD_OP op and will queue it
|
|
|
|
1. in wait_for_all_missing if it is a CEPH_OSD_OP_PGLS for a designated snapid and some object updates are still missing
|
|
2. in waiting_for_active if the op may write but the scrubber is working
|
|
3. in waiting_for_missing_object if the op requires an object or a snapdir or a specific snap that is still missing
|
|
4. in waiting_for_degraded_object if the op may write an object or a snapdir that is degraded, or if another object blocks it ("blocked_by")
|
|
5. in waiting_for_backfill_pos if the op requires an object that will be available after the backfill is complete
|
|
6. in waiting_for_ack if an ack from another OSD is expected
|
|
7. in waiting_for_ondisk if the op is waiting for a write to complete
|
|
|
|
Peering Messages
|
|
----------------
|
|
See OSD::handle_pg_(notify|info|log|query)
|
|
|
|
Peering messages are tagged with two epochs:
|
|
|
|
1. epoch_sent: map epoch at which the message was sent
|
|
2. query_epoch: map epoch at which the message triggering the message was sent
|
|
|
|
These are the same in cases where there was no triggering message. We discard
|
|
a peering message if the message's query_epoch if the PG in question has entered
|
|
a new epoch (See PG::old_peering_evt, PG::queue_peering_event). Notifies,
|
|
infos, notifies, and logs are all handled as PG::RecoveryMachine events and
|
|
are wrapped by PG::queue_* by PG::CephPeeringEvts, which include the created
|
|
state machine event along with epoch_sent and query_epoch in order to
|
|
generically check PG::old_peering_message upon insertion and removal from the
|
|
queue.
|
|
|
|
Note, notifies, logs, and infos can trigger the creation of a PG. See
|
|
OSD::get_or_create_pg.
|
|
|
|
|