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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_r368326097
 
 

 ##########
 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. 
 
 Review comment:
   Suggested re-wording to something like the following:
   ```
   Hints are a data repair technique applied during write operations. When         
   replica nodes are unavailable to accept a mutation, either due to failure or    
   more commonly routine maintenance, coordinators attempting to write to those    
   replicas store temporary hints on their local filesystem for later application  
   to the unavailable replica. Hints are an important way to help reduce the       
   duration of data inconsistency between replicas as they replay quickly after    
   unavailable nodes return to the ring, however they are best effort and do not   
   guarantee eventual consistency like :ref:`anti-entropy repair <repair>` does. 
   ```

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