Merge pull request #643 from elastic/GlenRSmith-patch-1

Add synced flush

Author: GlenRSmith

520_Post_Deployment/40_rolling_restart.asciidoc

@@ -20,9 +20,14 @@ What we want to do is tell Elasticsearch to hold off on rebalancing, because
 we have more knowledge about the state of the cluster due to external factors.
 The procedure is as follows:
 
-1. If possible, stop indexing new data.  This is not always possible, but will
+1. If possible, stop indexing new data and perform a synced flush.  This is not always possible, but will
 help speed up recovery time.
-
+A synced flush request is a “best effort” operation. It will fail if there are any pending indexing operations, but it is safe to reissue the request multiple times if necessary.
++
+[source,js]
+----
+POST /_flush/synced
+----
 2. Disable shard allocation.  This prevents Elasticsearch from rebalancing
 missing shards until you tell it otherwise.  If you know the maintenance window will be
 short, this is a good idea.  You can disable allocation as follows: