Francisco Fernández Castaño b4044004aa
Add recovery state tracking for Searchable Snapshots ()
This pull request adds recovery state tracking for Searchable Snapshots.

In order to track recoveries for searchable snapshot backed indices, this pull
request adds a new type of RecoveryState.
This newRecoveryState instance is able to deal with the
small differences that arise during Searchable snapshots recoveries.

Those differences can be summarized as follows:

-  The Directory implementation that's provided by SearchableSnapshots mark the
    snapshot files as reused during recovery. In order to keep track of the
    recovery process as the cache is pre-warmed, those files shouldn't be marked
    as reused.
 - Once the shard is created, the cache starts its pre-warming phase, meaning that
    we should keep track of those downloads during that process and tie the recovery
    to this pre-warming phase. The shard is considered recovered once this pre-warming
    phase has finished.

Backport of 
2020-08-05 17:41:49 +02:00
..