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https://issues.apache.org/jira/browse/FLINK-9377?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16629470#comment-16629470
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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_r220727617
##########
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);
+ } catch (ClassNotFoundException e) {
+ throw new IOException(
+ "Could not find requested
TypeSerializerConfigSnapshot class "
+ + serializerConfigClassname +
" in classpath.", e);
+ }
+
+ serializerConfigSnapshot =
InstantiationUtil.instantiate(serializerConfigSnapshotClass);
+
serializerConfigSnapshot.setUserCodeClassLoader(userCodeClassLoader);
Review comment:
The separation between `setUserCodeClassLoader(userCodeClassLoader);` and
`read(in)` seems a bit unclean, the methods always require to be used in
conjunction. It also leads a field "classloader" in the snapshot which is
sometimes set and sometimes not.
That is typically an indication that this should be one method: `read(in,
classloader)`. That does not match the `IOReadableWritable` interface, but I
see not why the config snapshots need to have that specific interface. They
could simply define their own interface.
If this blows the scope of this change, I would suggest to plan a followup
to clean this up.
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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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