Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/17902#discussion_r141079536
--- Diff:
common/kvstore/src/main/java/org/apache/spark/kvstore/KVStore.java ---
@@ -0,0 +1,129 @@
+/*
+ * 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.
+ */
+
+package org.apache.spark.kvstore;
+
+import java.io.Closeable;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.NoSuchElementException;
+
+/**
+ * Abstraction for a local key/value store for storing app data.
+ *
+ * <p>
+ * There are two main features provided by the implementations of this
interface:
+ * </p>
+ *
+ * <h3>Serialization</h3>
+ *
+ * <p>
+ * If the underlying data store requires serialization, data will be
serialized to and deserialized
+ * using a {@link KVStoreSerializer}, which can be customized by the
application. The serializer is
+ * based on Jackson, so it supports all the Jackson annotations for
controlling the serialization of
+ * app-defined types.
+ * </p>
+ *
+ * <p>
+ * Data is also automatically compressed to save disk space.
+ * </p>
+ *
+ * <h3>Automatic Key Management</h3>
--- End diff --
it will be better to have some examples, as I get confused here. What does
`Automatic` mean? I thought users have to provide a natural index.
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