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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-9808) Implement state conversion procedure in state backends
Date Wed, 24 Oct 2018 12:16:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-9808?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16662204#comment-16662204

ASF GitHub Bot commented on FLINK-9808:

StefanRRichter commented on a change in pull request #6875: [FLINK-9808] [state backends]
Migrate state when necessary in state backends
URL: https://github.com/apache/flink/pull/6875#discussion_r227761120

 File path: flink-runtime/src/test/java/org/apache/flink/runtime/state/StateBackendMigrationTestBase.java
 @@ -0,0 +1,780 @@
+ * 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.api.common.JobID;
+import org.apache.flink.api.common.state.ValueState;
+import org.apache.flink.api.common.state.ValueStateDescriptor;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.api.common.typeutils.TypeSerializerSchemaCompatibility;
+import org.apache.flink.api.common.typeutils.TypeSerializerSnapshot;
+import org.apache.flink.api.common.typeutils.base.IntSerializer;
+import org.apache.flink.core.memory.DataInputView;
+import org.apache.flink.core.memory.DataOutputView;
+import org.apache.flink.runtime.checkpoint.CheckpointOptions;
+import org.apache.flink.runtime.checkpoint.StateObjectCollection;
+import org.apache.flink.runtime.execution.Environment;
+import org.apache.flink.runtime.operators.testutils.DummyEnvironment;
+import org.apache.flink.types.StringValue;
+import org.apache.flink.util.TestLogger;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import java.io.IOException;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.RunnableFuture;
+import static org.junit.Assert.assertEquals;
+ * Tests for the {@link KeyedStateBackend} and {@link OperatorStateBackend} as produced
+ * by various {@link StateBackend}s.
+ */
+public abstract class StateBackendMigrationTestBase<B extends AbstractStateBackend>
extends TestLogger {
 Review comment:
   Overall, I find that this test tailored too much towards specific implementation details,
like how many times a certain serializer is called and when. Learning from past mistakes,
I found that such tests have a tendency to break fast under future changes and wrongly produce
test failures in the absence of real bugs.
   I would prefer if we could take a more "black box" approach, for example maybe taking one
more checkpoint/restore cycle and providing a clearly incompatibel serializer to see if the
state was migrated for the checkpoint. This is more stable against changes and tests what
we actually want to make sure.

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> Implement state conversion procedure in state backends
> ------------------------------------------------------
>                 Key: FLINK-9808
>                 URL: https://issues.apache.org/jira/browse/FLINK-9808
>             Project: Flink
>          Issue Type: Sub-task
>          Components: State Backends, Checkpointing
>            Reporter: Tzu-Li (Gordon) Tai
>            Assignee: Aljoscha Krettek
>            Priority: Critical
>              Labels: pull-request-available
>             Fix For: 1.7.0
> With FLINK-9377 in place and that config snapshots serve as the single source of truth
for recreating restore serializers, the next step would be to utilize this when performing
a full-pass state conversion (i.e., read with old / restore serializer, write with new serializer).
> For Flink's heap-based backends, it can be seen that state conversion inherently happens,
since all state is always deserialized after restore with the restore serializer, and written
with the new serializer on snapshots.
> For the RocksDB state backend, since state is lazily deserialized, state conversion needs
to happen for per-registered state on their first access if the registered new serializer
has a different serialization schema than the previous serializer.
> This task should consist of three parts:
> 1. Allow {{CompatibilityResult}} to correctly distinguish between whether the new serializer's
schema is a) compatible with the serializer as it is, b) compatible after the serializer has
been reconfigured, or c) incompatible.
> 2. Introduce state conversion procedures in the RocksDB state backend. This should occur
on the first state access.
> 3. Make sure that all other backends no longer do redundant serializer compatibility
checks. That is not required because those backends always perform full-pass state conversions.

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