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From GitBox <...@apache.org>
Subject [GitHub] [cassandra] jolynch commented on a change in pull request #419: Hints
Date Mon, 20 Jan 2020 02:42:29 GMT
jolynch commented on a change in pull request #419: Hints
URL: https://github.com/apache/cassandra/pull/419#discussion_r368326938
 
 

 ##########
 File path: doc/source/operating/hints.rst
 ##########
 @@ -1,22 +1,184 @@
-.. Licensed to the Apache Software Foundation (ASF) under one
-.. or more contributor license agreements.  See the NOTICE file
-.. distributed with this work for additional information
-.. regarding copyright ownership.  The ASF licenses this file
-.. to you under the Apache License, Version 2.0 (the
-.. "License"); you may not use this file except in compliance
-.. with the License.  You may obtain a copy of the License at
-..
-..     http://www.apache.org/licenses/LICENSE-2.0
-..
-.. Unless required by applicable law or agreed to in writing, software
-.. distributed under the License is distributed on an "AS IS" BASIS,
-.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-.. See the License for the specific language governing permissions and
-.. limitations under the License.
-
-.. highlight:: none
-
-Hints
------
-
-.. todo:: todo
+.. Licensed to the Apache Software Foundation (ASF) under one
+.. or more contributor license agreements.  See the NOTICE file
+.. distributed with this work for additional information
+.. regarding copyright ownership.  The ASF licenses this file
+.. to you under the Apache License, Version 2.0 (the
+.. "License"); you may not use this file except in compliance
+.. with the License.  You may obtain a copy of the License at
+..
+..     http://www.apache.org/licenses/LICENSE-2.0
+..
+.. Unless required by applicable law or agreed to in writing, software
+.. distributed under the License is distributed on an "AS IS" BASIS,
+.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+.. See the License for the specific language governing permissions and
+.. limitations under the License.
+
+.. highlight:: none
+
+Hints
+=====
+
+Hints are a type of repair during a write operation. At times a write or an update cannot
be replicated to all nodes satisfying the replication factor because a replica node is unavailable.
Under such a condition the mutation (a write or update) is stored temporarily on the coordinator
node in its filesystem. 
+
+Hints are metadata associated with a mutation (a write or update) indicating that the mutation
is not placed on a replica node (the target node) it is meant to be placed on because the
node is temporarily unavailable, or is unresponsive.  Hints are used to implement the eventual
consistency guarantee that all updates are eventually received by all replicas and all replicas
are eventually made consistent.    When the replica node becomes available the hints are replayed
on the node.
 
 Review comment:
   I'd slightly modify
   ```
   Hints are used to implement the eventual consistency guarantee ...
   ```
   to be
   ```
   Hints are one of the primary ways Cassandra implements the eventual consistency guarantee
...
   ```

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