ASF GitHub Bot commented on FLINK-8547:

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

    --- Diff: 
    @@ -0,0 +1,194 @@
    + * 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
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    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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    + */
    +package org.apache.flink.streaming.runtime.io;
    +import org.apache.flink.core.memory.MemorySegment;
    +import org.apache.flink.core.memory.MemorySegmentFactory;
    +import org.apache.flink.runtime.checkpoint.CheckpointMetaData;
    +import org.apache.flink.runtime.checkpoint.CheckpointMetrics;
    +import org.apache.flink.runtime.checkpoint.CheckpointOptions;
    +import org.apache.flink.runtime.io.network.api.CancelCheckpointMarker;
    +import org.apache.flink.runtime.io.network.api.CheckpointBarrier;
    +import org.apache.flink.runtime.io.network.api.EndOfPartitionEvent;
    +import org.apache.flink.runtime.io.network.buffer.Buffer;
    +import org.apache.flink.runtime.io.network.buffer.FreeingBufferRecycler;
    +import org.apache.flink.runtime.io.network.buffer.NetworkBuffer;
    +import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
    +import org.apache.flink.runtime.operators.testutils.DummyEnvironment;
    +import org.hamcrest.BaseMatcher;
    +import org.hamcrest.Description;
    +import java.util.Random;
    +import static org.junit.Assert.assertEquals;
    +import static org.junit.Assert.assertNotNull;
    +import static org.junit.Assert.assertTrue;
    + * Utility class containing common methods for testing
    + * {@link BufferSpillerTest} and {@link CreditBasedBufferBlockerTest}.
    + */
    +public class BarrierBufferTestBase {
    --- End diff --
    This is not exactly what I had in mind by deduplication of 
`BarrierBufferTest` and `CreditBasedBarrierBufferTest`.  Both of those tests 
are still pretty much copy of one another and those static methods are only a 
fraction of duplication.
    Look for example at the `testSingleChannelNoBarriers()` they are 99% 
identical. All of it's code could be moved to `BarrierBufferTestBase`. 
`BarrierBufferTestBase` would only need to define abstract method 
`CheckpointBarrierHandler createBarrierHandler()` which would be define 
differently in `BarrierBufferTest` and `CreditBasedBarrierBufferTest`. One 
minor thing is that `BarrierBufferTest` would need `checkNoTempFilesRemain()` 
added as an `@After` test hook. Same applies to all of the other tests.

> Implement CheckpointBarrierHandler not to spill data for exactly-once based 
> on credit-based flow control
> --------------------------------------------------------------------------------------------------------
>                 Key: FLINK-8547
>                 URL: https://issues.apache.org/jira/browse/FLINK-8547
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Network
>    Affects Versions: 1.5.0
>            Reporter: zhijiang
>            Assignee: zhijiang
>            Priority: Major
> Currently in exactly-once mode, the {{BarrierBuffer}} would block inputs with 
> barriers until all inputs have received the barrier for a given checkpoint. 
> To avoid back-pressuring the input streams which may cause distributed 
> deadlocks, the {{BarrierBuffer}} has to spill the data in disk files to 
> recycle the buffers for blocked channels.
> Based on credit-based flow control, every channel has exclusive buffers, so 
> it is no need to spill data for avoiding deadlock. Then we implement a new 
> {{CheckpointBarrierHandler}} for only buffering the data for blocked channels 
> for better performance.
> And this new {{CheckpointBarrierHandler}} can also be configured to use or 
> not in order to rollback the original mode for unexpected risks.

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