Github user amberarrow commented on a diff in the pull request:
https://github.com/apache/incubator-apex-malhar/pull/145#discussion_r57249937
--- Diff:
library/src/main/java/com/datatorrent/lib/state/BucketedState.java ---
@@ -0,0 +1,60 @@
+/**
+ * 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 com.datatorrent.lib.state;
+
+import java.util.concurrent.Future;
+
+import com.datatorrent.netlet.util.Slice;
+
+/**
+ * A state where keys are grouped in buckets.
+ */
+public interface BucketedState
+{
+ /**
+ * Sets the value of the key in bucket identified by bucketId.
+ *
+ * @param bucketId identifier of the bucket.
+ * @param key key
+ * @param value value
+ */
+ void put(long bucketId, Slice key, Slice value);
+
+ /**
+ * Returns the value of the key in a bucket identified by bucketId.
Fetching a key can be expensive if the key
+ * is not in memory and is present on disk. This fetches the key
synchronously. <br/>
+ * {@link #getAsync(long, Slice)} is recommended for efficiently reading
the value of a key.
+ *
+ * @param bucketId identifier of the bucket.
+ * @param key key
+ * @return value
+ */
+ Slice getSync(long bucketId, Slice key);
+
+ /**
+ * Returns the future using which the value is obtained.<br/>
+ * If the key is present in memory, then the future has its value set
when constructed.
--- End diff --
Oh, I misunderstood the comment.
If the intent is to say "If the key is present in memory, then the future
has its value set when constructed; if not the value is set some time after
construction"
(where I've added the part after the semicolon), then isn't this an
implementation detail that is better placed in the implementation file ?
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