Armin Braun 81e96954d0
Improve Efficiency of SnapshotsService CS Apply (#56874) (#59508)
This change removes the redundant submitting of two separate cluster state updates
for the node configuration changes and routing changes that affect snapshots.
Since we submitted the task to deal with node configuration changes every time on master
fail-over we could also move the BwC cleanup loop that removes `INIT` state snapshots as well
as snapshots that have all their shards completed into this cluster state update task.

Aside from improving efficiency overall this change has the fortunate side effect of moving
all snapshot finalization to the CS update thread. This is helpful for concurrent snapshots
since it makes it very natural and straight forward to order snapshot finalizations by exploiting
that they are all initiated on the same thread.
2020-07-14 11:49:09 +02:00
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