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diff --git a/src/ceph/doc/dev/osd_internals/backfill_reservation.rst b/src/ceph/doc/dev/osd_internals/backfill_reservation.rst deleted file mode 100644 index cf9dab4..0000000 --- a/src/ceph/doc/dev/osd_internals/backfill_reservation.rst +++ /dev/null @@ -1,38 +0,0 @@ -==================== -Backfill Reservation -==================== - -When a new osd joins a cluster, all pgs containing it must eventually backfill -to it. If all of these backfills happen simultaneously, it would put excessive -load on the osd. osd_max_backfills limits the number of outgoing or -incoming backfills on a single node. The maximum number of outgoing backfills is -osd_max_backfills. The maximum number of incoming backfills is -osd_max_backfills. Therefore there can be a maximum of osd_max_backfills * 2 -simultaneous backfills on one osd. - -Each OSDService now has two AsyncReserver instances: one for backfills going -from the osd (local_reserver) and one for backfills going to the osd -(remote_reserver). An AsyncReserver (common/AsyncReserver.h) manages a queue -by priority of waiting items and a set of current reservation holders. When a -slot frees up, the AsyncReserver queues the Context* associated with the next -item on the highest priority queue in the finisher provided to the constructor. - -For a primary to initiate a backfill, it must first obtain a reservation from -its own local_reserver. Then, it must obtain a reservation from the backfill -target's remote_reserver via a MBackfillReserve message. This process is -managed by substates of Active and ReplicaActive (see the substates of Active -in PG.h). The reservations are dropped either on the Backfilled event, which -is sent on the primary before calling recovery_complete and on the replica on -receipt of the BackfillComplete progress message), or upon leaving Active or -ReplicaActive. - -It's important that we always grab the local reservation before the remote -reservation in order to prevent a circular dependency. - -We want to minimize the risk of data loss by prioritizing the order in -which PGs are recovered. The highest priority is log based recovery -(OSD_RECOVERY_PRIORITY_MAX) since this must always complete before -backfill can start. The next priority is backfill of degraded PGs and -is a function of the degradation. A backfill for a PG missing two -replicas will have a priority higher than a backfill for a PG missing -one replica. The lowest priority is backfill of non-degraded PGs. |