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https://issues.apache.org/jira/browse/FLINK-6034?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15936307#comment-15936307
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ASF GitHub Bot commented on FLINK-6034:
---------------------------------------
Github user StefanRRichter commented on a diff in the pull request:
https://github.com/apache/flink/pull/3531#discussion_r107409091
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/KeyedStateHandle.java
---
@@ -0,0 +1,33 @@
+/*
+ * 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;
+
+/**
+ * A snapshot in keyed streams. Each {@code KeyedStateHandle} contains the
--- End diff --
A state handle typically means a pointer to some state. It will mostly be
used for snapshots of state backends, but conceptional this i a different level
of abstraction. I suggest to slightly modify this comment, moving away from the
concrete implementations of snapshots, to the concept of having a pointer to
serialized keyed state.
> Add KeyedStateHandle for the snapshots in keyed streams
> -------------------------------------------------------
>
> Key: FLINK-6034
> URL: https://issues.apache.org/jira/browse/FLINK-6034
> Project: Flink
> Issue Type: Sub-task
> Components: State Backends, Checkpointing
> Reporter: Xiaogang Shi
> Assignee: Xiaogang Shi
>
> Currently, the only type of the snapshots in keyed streams is
> {{KeyGroupsStateHandle}} which is full and store the states one group after
> another. With the introduction of incremental checkpointing, we need a higher
> level abstraction of keyed snapshots to allow flexible snapshot formats.
> The implementation of {{KeyedStateHandle}} s may vary a lot in different
> backends. The only information needed in {{KeyedStateHandle}} s is their key
> group range. When recovering the job with a different degree of parallelism,
> {{KeyedStateHandle}} s will be assigned to those subtasks whose key group
> ranges overlap with their ranges.
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