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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-9377) Remove writing serializers as part of the checkpoint meta information
Date Mon, 08 Oct 2018 11:11:01 GMT

    [ https://issues.apache.org/jira/browse/FLINK-9377?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16641666#comment-16641666
] 

ASF GitHub Bot commented on FLINK-9377:
---------------------------------------

dawidwys 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_r223310411
 
 

 ##########
 File path: flink-core/src/main/java/org/apache/flink/api/common/typeutils/TypeSerializerSnapshotSerializationUtil.java
 ##########
 @@ -0,0 +1,208 @@
+/*
+ * 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 javax.annotation.Nullable;
+import java.io.IOException;
+
+/**
+ * Utility methods for serialization of {@link TypeSerializerSnapshot}.
+ */
+public class TypeSerializerSnapshotSerializationUtil {
+
+	/**
+	 * Writes a {@link TypeSerializerSnapshot} to the provided data output view.
+	 *
+	 * <p>It is written with a format that can be later read again using
+	 * {@link #readSerializerSnapshot(DataInputView, ClassLoader, TypeSerializer)}.
+	 *
+	 * @param out the data output view
+	 * @param serializerSnapshot the serializer configuration snapshot to write
+	 * @param serializer the prior serializer. This needs to be written of the serializer snapshot
+	 *                   if the serializer snapshot is still the legacy {@link TypeSerializerConfigSnapshot}.
+	 *
+	 * @throws IOException
+	 */
+	public static <T> void writeSerializerSnapshot(
+		DataOutputView out,
+		TypeSerializerSnapshot<T> serializerSnapshot,
+		TypeSerializer<T> serializer) throws IOException {
+
+		new TypeSerializerSnapshotSerializationProxy<>(serializerSnapshot, serializer).write(out);
+	}
+
+	/**
+	 * Reads from a data input view a {@link TypeSerializerSnapshot} that was previously
+	 * written using {@link TypeSerializerSnapshotSerializationUtil#writeSerializerSnapshot(DataOutputView,
TypeSerializerSnapshot, TypeSerializer)}.
+	 *
+	 * @param in the data input view
+	 * @param userCodeClassLoader the user code class loader to use
+	 * @param existingPriorSerializer the prior serializer. This would only be non-null if we
are
+	 *                                restoring from a snapshot taken with Flink version <=
1.6.
+	 *
+	 * @return the read serializer configuration snapshot
+	 *
+	 * @throws IOException
+	 */
+	public static <T> TypeSerializerSnapshot<T> readSerializerSnapshot(
+			DataInputView in,
+			ClassLoader userCodeClassLoader,
+			@Nullable TypeSerializer<T> existingPriorSerializer) throws IOException {
+
+		final TypeSerializerSnapshotSerializationProxy<T> proxy =
+			new TypeSerializerSnapshotSerializationProxy<>(userCodeClassLoader, existingPriorSerializer);
+		proxy.read(in);
+
+		return proxy.getSerializerSnapshot();
+	}
+
+	/**
+	 * Utility serialization proxy for a {@link TypeSerializerSnapshot}.
+	 */
+	static final class TypeSerializerSnapshotSerializationProxy<T> extends VersionedIOReadableWritable
{
+
+		private static final int VERSION = 2;
+
+		private ClassLoader userCodeClassLoader;
+		private TypeSerializerSnapshot<T> serializerSnapshot;
+		private TypeSerializer<T> serializer;
+
+		TypeSerializerSnapshotSerializationProxy(
+			ClassLoader userCodeClassLoader,
+			@Nullable TypeSerializer<T> existingPriorSerializer) {
+			this.userCodeClassLoader = Preconditions.checkNotNull(userCodeClassLoader);
+			this.serializer = existingPriorSerializer;
+		}
+
+		TypeSerializerSnapshotSerializationProxy(
+			TypeSerializerSnapshot<T> serializerConfigSnapshot,
+			TypeSerializer<T> serializer) {
+			this.serializerSnapshot = Preconditions.checkNotNull(serializerConfigSnapshot);
+			this.serializer = Preconditions.checkNotNull(serializer);
+		}
+
+		/**
+		 * Binary format layout of a written serializer snapshot is as follows:
+		 *
+		 * <ul>
+		 *     <li>1. Serializer snapshot classname (UTF).</li>
+		 *     <li>2. The originating serializer of the snapshot, if any, written via Java
serialization.
+		 *         Presence of the serializer is indicated by a flag (boolean -> TypeSerializer).</li>
+		 *     <li>3. The version of the serializer snapshot's binary format.</li>
+		 *     <li>4. The actual serializer snapshot.</li>
+		 * </ul>
+		 */
+		@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(serializerSnapshot.getClass().getName());
+
+			if (serializerSnapshot instanceof TypeSerializerConfigSnapshot) {
+				// backwards compatible path, where the serializer snapshot is still using the
+				// deprecated interface; the originating serializer needs to be written to the byte stream
+				out.writeBoolean(true);
+				@SuppressWarnings("unchecked")
+				TypeSerializerConfigSnapshot<T> legacySerializerSnapshot = (TypeSerializerConfigSnapshot<T>)
serializerSnapshot;
+				TypeSerializerSerializationUtil.writeSerializer(out, serializer);
+
+				// TypeSerializerConfigSnapshot includes the version number implicitly when it is written
+				legacySerializerSnapshot.write(out);
+			} else {
+				out.writeBoolean(false);
+
+				out.writeInt(serializerSnapshot.getCurrentVersion());
+				serializerSnapshot.write(out);
+			}
+		}
+
+		@SuppressWarnings("unchecked")
+		@Override
+		public void read(DataInputView in) throws IOException {
+			super.read(in);
+
+			String serializerConfigClassname = in.readUTF();
+			Class<? extends TypeSerializerSnapshot> serializerConfigSnapshotClass;
+			try {
+				serializerConfigSnapshotClass = (Class<? extends TypeSerializerSnapshot>)
+					Class.forName(serializerConfigClassname, false, userCodeClassLoader);
+			} catch (ClassNotFoundException e) {
+				throw new IOException(
+					"Could not find requested TypeSerializerConfigSnapshot class "
+						+ serializerConfigClassname +  " in classpath.", e);
+			}
+
+			serializerSnapshot = InstantiationUtil.instantiate(serializerConfigSnapshotClass);
+
+			if (getReadVersion() >= 2) {
 
 Review comment:
   Could you add a few comments, which branch corresponds to which flink version/snapshot
version? This is quite important code block imho.

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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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