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https://issues.apache.org/jira/browse/FLINK-8360?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16322302#comment-16322302
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ASF GitHub Bot commented on FLINK-8360:
---------------------------------------
Github user pnowojski commented on a diff in the pull request:
https://github.com/apache/flink/pull/5239#discussion_r160929798
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/TaskStateManager.java
---
@@ -0,0 +1,62 @@
+/*
+ * 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;
+
+import org.apache.flink.runtime.checkpoint.CheckpointMetaData;
+import org.apache.flink.runtime.checkpoint.CheckpointMetrics;
+import org.apache.flink.runtime.checkpoint.OperatorSubtaskState;
+import org.apache.flink.runtime.checkpoint.TaskStateSnapshot;
+import org.apache.flink.runtime.jobgraph.OperatorID;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+/**
+ * This interface provides methods to report and retrieve state for a task.
+ *
+ * <p>When a checkpoint or savepoint is triggered on a task, it will
create snapshots for all stream operator instances
+ * it owns. All operator snapshots from the task are then reported via
this interface. A typical implementation will
+ * dispatch and forward the reported state information to interested
parties such as the checkpoint coordinator or a
+ * local state store.
+ *
+ * <p>This interface also offers the complementary method that provides
access to previously saved state of operator
+ * instances in the task for restore purposes.
+ */
+public interface TaskStateManager extends CheckpointListener {
--- End diff --
Disclaimer, despite this not being a nit, if you have strong objections I
will not fight over this comment :)
I think this class should be split into two:
1. `TaskStateReporter` that handles sending the messages to the master
(extracting and maybe wrapping `checkpointResponder` from this one)
2. and already existing `TaskLocalStateStore`
and use them separately. `StreamTask` would call:
```
localStateStore.store(...)
taskStateReporter.reportTaskStateSnapshots(...)
```
And all of the remaining usages of the `TaskStateManager` could be replaced
by calls to the `TaskLocalStateStore` directly.
One notable exception might be
`org.apache.flink.runtime.state.TaskStateManagerImpl#prioritizedOperatorState`
which is not present in this commit, but comes to live later on. It could
either be converted into static function (since it doesn't seem to have any
side effects) taking three parameters `(jobManagerTaskRestore,
localStateStore, operatorId)` or create some third entity
`TaskStateRestoreSelector`, `LocalAndRemoteTaskStateSelector`,
`OperatorStatePrioritizer` or something else.
I think that would let us get rid of one vague `Manager` class and replace
it with some smaller purpose build entities, which might be handy both for code
understanding, testing and refactoring in the future.
> Implement task-local state recovery
> -----------------------------------
>
> Key: FLINK-8360
> URL: https://issues.apache.org/jira/browse/FLINK-8360
> Project: Flink
> Issue Type: New Feature
> Components: State Backends, Checkpointing
> Reporter: Stefan Richter
> Assignee: Stefan Richter
> Fix For: 1.5.0
>
>
> This issue tracks the development of recovery from task-local state. The main
> idea is to have a secondary, local copy of the checkpointed state, while
> there is still a primary copy in DFS that we report to the checkpoint
> coordinator.
> Recovery can attempt to restore from the secondary local copy, if available,
> to save network bandwidth. This requires that the assignment from tasks to
> slots is as sticky is possible.
> For starters, we will implement this feature for all managed keyed states and
> can easily enhance it to all other state types (e.g. operator state) later.
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