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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=16641670#comment-16641670
] 

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_r223305539
 
 

 ##########
 File path: flink-core/src/main/java/org/apache/flink/api/common/typeutils/TypeSerializerSchemaCompatibility.java
 ##########
 @@ -0,0 +1,138 @@
+/*
+ * 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.annotation.PublicEvolving;
+import org.apache.flink.util.Preconditions;
+
+import javax.annotation.Nullable;
+
+/**
+ * A {@code TypeSerializerSchemaCompatibility} represents information about whether or not
a {@link TypeSerializer}
+ * can be safely used to read data written by a previous type serializer.
+ *
+ * <p>Typically, the compatibility of the new serializer is resolved by checking it
against the snapshotted
+ * {@link TypeSerializerConfigSnapshot} of the previous serializer. Depending on the type
of the
+ * resolved compatibility result, migration (i.e., reading bytes with the previous serializer
and then writing
+ * it again with the new serializer) may be required before the new serializer can be used.
+ *
+ * @param <T> the type of data serialized bythe serializer that was being checked.
 
 Review comment:
   `bythe` -> `by the`

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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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