anchor.diff:  [[indices-synced-flush]]
   === Synced Flush
   
  -Elasticsearch tracks the indexing activity of each shards. Shards that have not
  -received any indexing operations for 30 minutes (configurable) are automatically marked as inactive. This presents
  +Elasticsearch tracks the indexing activity of each shard. Shards that have not
  +received any indexing operations for 30 minutes are automatically marked as inactive. This presents
   an opportunity for Elasticsearch to reduce shard resources and also perform
  -a special kind of flush, called `synced flush`. A synced flush performs normal
  -flushing and adds a special uniquely generated marker (`sync_id`) to all shards.
  +a special kind of flush, called `synced flush`. A synced flush performs a normal flush, then adds
  +a generated unique marker (sync_id) to all shards.
   
   Since the sync id marker was added when there were no ongoing indexing operations, it can
  -be used as a quick way to check if two shards indices are identical. This quick sync id
  +be used as a quick way to check if the two shards' lucene indices are identical. This quick sync id
   comparison (if present) is used during recovery or restarts to skip the first and
   most costly phase of the process. In that case, no segment files need to be copied and
   the transaction log replay phase of the recovery can start immediately. Note that since the sync id
  -marker was applied together with a flush, it is highly likely that the transaction log will be empty,
  +marker was applied together with a flush, it is very likely that the transaction log will be empty,
   speeding up recoveries even more.
   
   This is particularly useful for use cases having lots of indices which are
   never or very rarely updated, such as time based data. This use case typically generates lots of indices whose
   recovery without the synced flush marker would take a long time.
   
  -To check whether a shard has a marker or not, one can use the `commit` section of shard stats returned by
  +To check whether a shard has a marker or not, look for the `commit` section of shard stats returned by
   the <<indices-stats,indices stats>> API:
   
   [source,bash]
  
positive.code: --------------------------------------------------
  
  
  The synced flush API can be applied to more than one index with a single call,
  or even on `_all` the indices.
  
  
negative.code: }
  --------------------------------------------------
  
  NOTE: The above error is shown when the synced flush failes due to concurrent indexing operations. The HTTP
  status code in that case will be `409 CONFLICT`.
  
  Sometimes the failures are specific to a shard copy. The copies that failed will not be eligible for
  fast recovery but those that succeeded still will be. This case is reported as follows:
  