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https://issues.apache.org/jira/browse/FLINK-9377?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16629476#comment-16629476
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ASF GitHub Bot commented on FLINK-9377:
---------------------------------------
StephanEwen commented on a change in pull request #6711: [FLINK-9377] [core,
state backends] Remove serializers from checkpoints
URL: https://github.com/apache/flink/pull/6711#discussion_r220738283
##########
File path:
flink-core/src/main/java/org/apache/flink/api/common/typeutils/TypeSerializerConfigSnapshotSerializationUtil.java
##########
@@ -0,0 +1,172 @@
+/*
+ * 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.api.common.typeutils;
+
+import org.apache.flink.core.io.VersionedIOReadableWritable;
+import org.apache.flink.core.memory.DataInputView;
+import org.apache.flink.core.memory.DataOutputView;
+import org.apache.flink.util.InstantiationUtil;
+import org.apache.flink.util.Preconditions;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Utility methods for serialization of {@link TypeSerializerConfigSnapshot}.
+ */
+public class TypeSerializerConfigSnapshotSerializationUtil {
+
+ /**
+ * Writes a {@link TypeSerializerConfigSnapshot} to the provided data
output view.
+ *
+ * <p>It is written with a format that can be later read again using
+ * {@link #readSerializerConfigSnapshot(DataInputView, ClassLoader)}.
+ *
+ * @param out the data output view
+ * @param serializerConfigSnapshot the serializer configuration
snapshot to write
+ *
+ * @throws IOException
+ */
+ public static <T> void writeSerializerConfigSnapshot(
+ DataOutputView out,
+ TypeSerializerConfigSnapshot<T> serializerConfigSnapshot,
+ TypeSerializer<T> serializer) throws IOException {
+
+ new
TypeSerializerConfigSnapshotSerializationProxy<>(serializerConfigSnapshot,
serializer).write(out);
+ }
+
+ /**
+ * Reads from a data input view a {@link TypeSerializerConfigSnapshot}
that was previously
+ * written using {@link
TypeSerializerConfigSnapshotSerializationUtil#writeSerializerConfigSnapshot(DataOutputView,
TypeSerializerConfigSnapshot, TypeSerializer)}.
+ *
+ * @param in the data input view
+ * @param userCodeClassLoader the user code class loader to use
+ *
+ * @return the read serializer configuration snapshot
+ *
+ * @throws IOException
+ */
+ public static TypeSerializerConfigSnapshot readSerializerConfigSnapshot(
+ DataInputView in,
+ ClassLoader userCodeClassLoader) throws IOException {
+
+ final TypeSerializerConfigSnapshotSerializationProxy proxy =
new TypeSerializerConfigSnapshotSerializationProxy(userCodeClassLoader);
+ proxy.read(in);
+
+ return proxy.getSerializerConfigSnapshot();
+ }
+
+ /**
+ * Reads from a data input view multiple {@link
TypeSerializerConfigSnapshot}s that was previously
+ * written using {@link
TypeSerializerConfigSnapshotSerializationUtil#writeSerializerConfigSnapshot(DataOutputView,
TypeSerializerConfigSnapshot, TypeSerializer)}.
+ *
+ * @param in the data input view
+ * @param userCodeClassLoader the user code class loader to use
+ *
+ * @return the read serializer configuration snapshots
+ *
+ * @throws IOException
+ */
+ public static List<TypeSerializerConfigSnapshot<?>>
readSerializerConfigSnapshots(
+ DataInputView in,
+ ClassLoader userCodeClassLoader) throws IOException {
+
+ int numFields = in.readInt();
+ final List<TypeSerializerConfigSnapshot<?>>
serializerConfigSnapshots = new ArrayList<>(numFields);
+
+ TypeSerializerConfigSnapshotSerializationProxy proxy;
+ for (int i = 0; i < numFields; i++) {
+ proxy = new
TypeSerializerConfigSnapshotSerializationProxy(userCodeClassLoader);
+ proxy.read(in);
+
serializerConfigSnapshots.add(proxy.getSerializerConfigSnapshot());
+ }
+
+ return serializerConfigSnapshots;
+ }
+
+ /**
+ * Utility serialization proxy for a {@link
TypeSerializerConfigSnapshot}.
+ */
+ static final class TypeSerializerConfigSnapshotSerializationProxy<T>
extends VersionedIOReadableWritable {
+
+ private static final int VERSION = 1;
+
+ private ClassLoader userCodeClassLoader;
+ private TypeSerializerConfigSnapshot<T>
serializerConfigSnapshot;
+ private TypeSerializer<T> serializer;
+
+ TypeSerializerConfigSnapshotSerializationProxy(ClassLoader
userCodeClassLoader) {
+ this.userCodeClassLoader =
Preconditions.checkNotNull(userCodeClassLoader);
+ }
+
+ TypeSerializerConfigSnapshotSerializationProxy(
+ TypeSerializerConfigSnapshot<T>
serializerConfigSnapshot,
+ TypeSerializer<T> serializer) {
+ this.serializerConfigSnapshot =
Preconditions.checkNotNull(serializerConfigSnapshot);
+ this.serializer =
Preconditions.checkNotNull(serializer);
+ }
+
+ @Override
+ public void write(DataOutputView out) throws IOException {
+ super.write(out);
+
+ // config snapshot class, so that we can re-instantiate
the
+ // correct type of config snapshot instance when
deserializing
+
out.writeUTF(serializerConfigSnapshot.getClass().getName());
+
+ // TODO this is a temporary workaround until all
serializer config snapshot classes in Flink
+ // TODO have properly implemented the restore
serializer factory methods
+ serializerConfigSnapshot.setSerializer(serializer);
+
+ // the actual configuration parameters
+ serializerConfigSnapshot.write(out);
+ }
+
+ @SuppressWarnings("unchecked")
+ @Override
+ public void read(DataInputView in) throws IOException {
+ super.read(in);
+
+ String serializerConfigClassname = in.readUTF();
+ Class<? extends TypeSerializerConfigSnapshot>
serializerConfigSnapshotClass;
+ try {
+ serializerConfigSnapshotClass = (Class<?
extends TypeSerializerConfigSnapshot>)
+
Class.forName(serializerConfigClassname, true, userCodeClassLoader);
Review comment:
Minor: I found it often better to not initialize the class when reflectively
loading it (pass false instead of true). Initialization will then happen on
first access.
That means that errors during static initialization happen not in the
deserialization stack, but upon use of the class later, which is often a bit
easier to understand.
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> Remove writing serializers as part of the checkpoint meta information
> ---------------------------------------------------------------------
>
> Key: FLINK-9377
> URL: https://issues.apache.org/jira/browse/FLINK-9377
> Project: Flink
> Issue Type: Sub-task
> Components: State Backends, Checkpointing
> Reporter: Tzu-Li (Gordon) Tai
> Assignee: Tzu-Li (Gordon) Tai
> Priority: Critical
> Labels: pull-request-available
> Fix For: 1.7.0
>
>
> When writing meta information of a state in savepoints, we currently write
> both the state serializer as well as the state serializer's configuration
> snapshot.
> Writing both is actually redundant, as most of the time they have identical
> information.
> Moreover, the fact that we use Java serialization to write the serializer
> and rely on it to be re-readable on the restore run, already poses problems
> for serializers such as the {{AvroSerializer}} (see discussion in FLINK-9202)
> to perform even a compatible upgrade.
> The proposal here is to leave only the config snapshot as meta information,
> and use that as the single source of truth of information about the schema of
> serialized state.
> The config snapshot should be treated as a factory (or provided to a
> factory) to re-create serializers capable of reading old, serialized state.
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