Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/3483#discussion_r106138099
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/heap/CopyOnWriteStateTable.java
---
@@ -0,0 +1,1021 @@
+/*
+ * 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.flink.runtime.state.heap;
+
+import org.apache.flink.annotation.VisibleForTesting;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.runtime.state.RegisteredBackendStateMetaInfo;
+import org.apache.flink.runtime.state.StateTransformationFunction;
+import org.apache.flink.util.MathUtils;
+import org.apache.flink.util.Preconditions;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Arrays;
+import java.util.ConcurrentModificationException;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.TreeSet;
+
+/**
+ * Basis for Flink's in-memory state tables with copy-on-write support.
This map does not support null values for
+ * key or namespace.
+ * <p>
+ * StateTable sacrifices some peak performance and memory efficiency for
features like incremental rehashing and
+ * asynchronous snapshots through copy-on-write. Copy-on-write tries to
minimize the amount of copying by maintaining
+ * version meta data for both, the map structure and the state objects.
However, we must often proactively copy state
+ * objects when we hand them to the user.
+ * <p>
+ * As for any state backend, user should not keep references on state
objects that they obtained from state backends
+ * outside the scope of the user function calls.
+ * <p>
+ * Some brief maintenance notes:
+ * <p>
+ * 1) Flattening the underlying data structure from a nested maps
(namespace) -> (key) -> (state) to one flat map
--- End diff --
Lose the `a` in `from a nested maps`, I think.
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