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https://issues.apache.org/jira/browse/FLINK-8790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16496462#comment-16496462
 ] 

ASF GitHub Bot commented on FLINK-8790:
---------------------------------------

Github user StefanRRichter commented on a diff in the pull request:

    https://github.com/apache/flink/pull/5582#discussion_r192081960
  
    --- Diff: 
flink-state-backends/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBIncrementalCheckpointUtils.java
 ---
    @@ -0,0 +1,80 @@
    +/*
    + * 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.contrib.streaming.state;
    +
    +import org.apache.flink.runtime.state.KeyGroupRange;
    +
    +import org.rocksdb.ColumnFamilyHandle;
    +import org.rocksdb.RocksDB;
    +import org.rocksdb.RocksDBException;
    +
    +import java.util.List;
    +
    +/**
    + * Utils for RocksDB Incremental Checkpoint.
    + */
    +public class RocksDBIncrementalCheckpointUtils {
    +
    +   public static void clipDBWithKeyGroupRange(
    +           RocksDB db,
    +           List<ColumnFamilyHandle> columnFamilyHandles,
    +           KeyGroupRange targetGroupRange,
    +           KeyGroupRange currentGroupRange,
    +           int keyGroupPrefixBytes) throws RocksDBException {
    +
    +           for (ColumnFamilyHandle columnFamilyHandle : 
columnFamilyHandles) {
    +                   if (currentGroupRange.getStartKeyGroup() < 
targetGroupRange.getStartKeyGroup()) {
    +                           byte[] beginKey = 
RocksDBKeySerializationUtils.serializeKeyGroup(
    +                                   currentGroupRange.getStartKeyGroup(), 
keyGroupPrefixBytes);
    +                           byte[] endKye = 
RocksDBKeySerializationUtils.serializeKeyGroup(
    +                                   targetGroupRange.getStartKeyGroup(), 
keyGroupPrefixBytes);
    +                           db.deleteRange(columnFamilyHandle, beginKey, 
endKye);
    +                   }
    +
    +                   if (currentGroupRange.getEndKeyGroup() > 
targetGroupRange.getEndKeyGroup()) {
    +                           byte[] beginKey = 
RocksDBKeySerializationUtils.serializeKeyGroup(
    +                                   targetGroupRange.getEndKeyGroup() + 1, 
keyGroupPrefixBytes);
    +
    +                           byte[] endKey = new byte[keyGroupPrefixBytes];
    +                           for (int i = 0; i < keyGroupPrefixBytes; ++i) {
    +                                   endKey[i] = (byte) (0xFF);
    +                           }
    +                           db.deleteRange(columnFamilyHandle, beginKey, 
endKey);
    +                   }
    +           }
    +   }
    +
    +   public static int evaluateGroupRange(KeyGroupRange range1, 
KeyGroupRange range2) {
    --- End diff --
    
    Then let's just keep it simple for now, and we can still improve it if we 
later find that the size can also be an indicator of the better initial db 
state.


> Improve performance for recovery from incremental checkpoint
> ------------------------------------------------------------
>
>                 Key: FLINK-8790
>                 URL: https://issues.apache.org/jira/browse/FLINK-8790
>             Project: Flink
>          Issue Type: Improvement
>          Components: State Backends, Checkpointing
>    Affects Versions: 1.5.0
>            Reporter: Sihua Zhou
>            Assignee: Sihua Zhou
>            Priority: Major
>             Fix For: 1.6.0
>
>
> When there are multi state handle to be restored, we can improve the 
> performance as follow:
> 1. Choose the best state handle to init the target db
> 2. Use the other state handles to create temp db, and clip the db according 
> to the target key group range (via rocksdb.deleteRange()), this can help use 
> get rid of the `key group check` in 
>  `data insertion loop` and also help us get rid of traversing the useless 
> record.



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