Github user StefanRRichter commented on a diff in the pull request:
https://github.com/apache/flink/pull/4353#discussion_r133026125
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/checkpoint/TaskStateSnapshot.java
---
@@ -0,0 +1,139 @@
+/*
+ * 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.checkpoint;
+
+import org.apache.flink.runtime.jobgraph.OperatorID;
+import org.apache.flink.runtime.state.CompositeStateHandle;
+import org.apache.flink.runtime.state.SharedStateRegistry;
+import org.apache.flink.runtime.state.StateUtil;
+import org.apache.flink.util.Preconditions;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * This class encapsulates state handles to the snapshots of all operator
instances executed within one task. A task
+ * can run multiple operator instances as a result of operator chaining,
and all operator instances from the chain can
+ * register their state under their operator id. Each operator instance is
a physical execution responsible for
+ * processing a partition of the data that goes through a logical
operator. This partitioning happens to parallelize
+ * execution of logical operators, e.g. distributing a map function.
+ *
+ * <p>One instance of this class contains the information that one task
will send to acknowledge a checkpoint request by
+ * the checkpoint coordinator. Tasks run operator instances in parallel,
so the union of all
+ * {@link TaskStateSnapshot} that are collected by the checkpoint
coordinator from all tasks represent the whole
+ * state of a job at the time of the checkpoint.
+ *
+ * <p>This class should be called TaskState once the old class with this
name that we keep for backwards
+ * compatibility goes away.
+ */
+public class TaskStateSnapshot implements CompositeStateHandle {
+
+ private static final long serialVersionUID = 1L;
+
+ /** Mapping from an operator id to the state of one subtask of this
operator */
+ private final Map<OperatorID, OperatorSubtaskState>
subtaskStatesByOperatorID;
--- End diff --
Hmm, I think if we consider default load factors and for large sizes, I
would pick a min >30% hit rate linear array scan over 100% hit rate random
access iteration. For all expected sizes (in cache) in this class, it should
not matter. LHM also consumes a bit more memory. I would tend to keep it this
way.
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