anchor.diff:  Other safeguards are tracked in the meta-issue {GIT}11511[#11511].
   
   [float]
  -=== The _version field may not uniquely identify document content during a network partition (STATUS: ONGOING)
  -
  -When a primary has been partitioned away from the cluster there is a short period of time until it detects this. During that time it will continue
  -indexing writes locally, thereby updating document versions. When it tries to replicate the operation, however, it will discover that it is
  -partitioned away. It won't acknowledge the write and will wait until the partition is resolved to negotiate with the master on how to proceed.
  -The master will decide to either fail any replicas which failed to index the operations on the primary or tell the primary that it has to
  -step down because a new primary has been chosen in the meantime. Since the old primary has already written documents, clients may already have read from
  -the old primary before it shuts itself down. The version numbers of these reads may not be unique if the new primary has already accepted
  -writes for the same document (see {GIT}19269[#19269]).
  -
  -We are currently implementing Sequence numbers {GIT}10708[#10708] which better track primary changes. Sequence numbers thus provide a basis
  -for uniquely identifying writes even in the presence of network partitions and will replace `_version` in operations that require this.
  -
  -[float]
   === Relocating shards omitted by reporting infrastructure (STATUS: ONGOING)
   
   Indices stats and indices segments requests reach out to all nodes that have shards of that index. Shards that have relocated from a node
  
positive.code: improvements throughout this page to provide the full context.
  
  If you’re interested in more on how we approach ensuring resiliency in
  Elasticsearch, you may be interested in Igor Motov’s recent talk
  http://www.elastic.co/videos/improving-elasticsearch-resiliency[Improving Elasticsearch Resiliency].
  
  You may also be interested in our blog post
  
negative.code: The new tests are run continuously in our testing farm and are passing. We are also working on running Jepsen independently to verify
  that no failures are found.
  
  == Completed
  
  [float]
  === Documents indexed during a network partition cannot be uniquely identified (STATUS: DONE, v7.0.0)
  
  When a primary has been partitioned away from the cluster there is a short
  period of time until it detects this. During that time it will continue
  indexing writes locally, thereby updating document versions. When it tries
  to replicate the operation, however, it will discover that it is partitioned
  away. It won't acknowledge the write and will wait until the partition is
  resolved to negotiate with the master on how to proceed. The master will
  decide to either fail any replicas which failed to index the operations on
  the primary or tell the primary that it has to step down because a new primary
  has been chosen in the meantime. Since the old primary has already written
  documents, clients may already have read from the old primary before it shuts
  itself down. The `_version` field of these reads may not uniquely identify the
  document's version if the new primary has already accepted writes for the same
  document (see {GIT}19269[#19269]).
  
  The Sequence numbers infrastructure {GIT}10708[#10708] has introduced more
  precise ways for tracking primary changes. This new infrastructure therefore
  provides a way for uniquely identifying documents using their primary term
  and sequence number fields, even in the presence of network partitions, and
  has been used to replace the `_version` field in operations that require
  uniquely identifying the document, such as optimistic concurrency control.
  
  [float]
  === Replicas can fall out of sync when a primary shard fails (STATUS: DONE, v7.0.0)
  
  When a primary shard fails, a replica shard will be promoted to be the primary
  shard. If there is more than one replica shard, it is possible for the
  remaining replicas to be out of sync with the new primary shard. This is caused
  by operations that were in-flight when the primary shard failed and may not
  have been processed on all replica shards. These discrepancies are not
  repaired on primary promotion but instead delayed until replica shards are
  relocated (e.g., from hot to cold nodes); this means that the length of time
  in which replicas can be out of sync with the primary shard is unbounded.
  
  Sequence numbers {GIT}10708[#10708] provide a mechanism for identifying
  the discrepancies between shard copies at the document level, which allows
  to efficiently sync up the remaining replicas with the newly-promoted primary
  shard.
  
  [float]
  === Repeated network partitions can cause cluster state updates to be lost (STATUS: DONE, v7.0.0)
  