[ 
https://issues.apache.org/jira/browse/FLINK-26050?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Piotr Nowojski updated FLINK-26050:
-----------------------------------
    Description: 
When using processing or event time windows, in some workloads, there will be a 
lot of small sst files(serveral KB) in rocksdb local directory and may cause 
"Too many files error".

Use rocksdb tool ldb to find out content in sst files:
 * column family of these small sst files is "processing_window-timers".
 * most sst files are in level-1.
 * records in sst files are almost kTypeDeletion.
 * creation time of sst file correspond to checkpoint interval.

These small sst files seem to be generated when flink checkpoint is triggered. 
Although all content in sst are delete tags, they are not compacted and deleted 
in rocksdb compaction because of not intersecting with each other(rocksdb 
[compaction trivial 
move|https://github.com/facebook/rocksdb/wiki/Compaction-Trivial-Move]). And 
there seems to be no chance to delete them because of small size and not 
intersect with other sst files.

 

I will attach a simple program to reproduce the problem.

 

Since timer in processing time window is generated in strictly ascending 
order(both put and delete). So If workload of job happen to generate level-0 
sst files not intersect with each other.(for example: processing window size 
much smaller than checkpoint interval, and no window content cross checkpoint 
interval or no new data in window crossing checkpoint interval). There will be 
many small sst files generated until job restored from savepoint, or 
incremental checkpoint is disabled. 

 

May be similar problem exists when user use timer in operators with same 
workload.

 

Code to reproduce the problem:
{code:java}
package org.apache.flink.jira;

import lombok.extern.slf4j.Slf4j;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.configuration.RestOptions;
import org.apache.flink.configuration.TaskManagerOptions;
import org.apache.flink.contrib.streaming.state.RocksDBStateBackend;
import org.apache.flink.streaming.api.TimeCharacteristic;
import org.apache.flink.streaming.api.checkpoint.ListCheckpointed;
import org.apache.flink.streaming.api.datastream.DataStreamSource;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.streaming.api.functions.source.SourceFunction;
import org.apache.flink.streaming.api.functions.windowing.ProcessWindowFunction;
import 
org.apache.flink.streaming.api.windowing.assigners.TumblingProcessingTimeWindows;
import org.apache.flink.streaming.api.windowing.time.Time;
import org.apache.flink.streaming.api.windowing.windows.TimeWindow;
import org.apache.flink.util.Collector;

import java.util.Collections;
import java.util.List;
import java.util.Random;

@Slf4j
public class StreamApp  {
  public static void main(String[] args) throws Exception {
    Configuration config = new Configuration();
    config.set(RestOptions.ADDRESS, "127.0.0.1");
    config.set(RestOptions.PORT, 10086);
    config.set(TaskManagerOptions.NUM_TASK_SLOTS, 6);
    new 
StreamApp().configureApp(StreamExecutionEnvironment.createLocalEnvironment(1, 
config));
  }

  public void configureApp(StreamExecutionEnvironment env) throws Exception {

    env.enableCheckpointing(20000); // 20sec

    RocksDBStateBackend rocksDBStateBackend =
        new 
RocksDBStateBackend("file:///Users/shenjiaqi/Workspace/jira/flink-51/checkpoints/",
 true); // need to be reconfigured
    
rocksDBStateBackend.setDbStoragePath("/Users/shenjiaqi/Workspace/jira/flink-51/flink/rocksdb_local_db");
 // need to be reconfigured

    env.setStateBackend(rocksDBStateBackend);
    env.getCheckpointConfig().setCheckpointTimeout(100000);
    env.getCheckpointConfig().setTolerableCheckpointFailureNumber(5);
    env.setParallelism(1);
    env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);

    env.getConfig().setTaskCancellationInterval(10000);

    for (int i = 0; i < 1; ++i) {
      createOnePipeline(env);
    }

    env.execute("StreamApp");
  }


  private void createOnePipeline(StreamExecutionEnvironment env) {
    // data source is configured so that little window cross checkpoint interval
    DataStreamSource<String> stream = env.addSource(new Generator(1, 3000, 
3600));

    stream.keyBy(x -> x)
        // make sure window size less than checkpoint interval. though 100ms is 
too small, I think increase this value can still reproduce the problem with 
longer time.
        .window(TumblingProcessingTimeWindows.of(Time.milliseconds(100)))
        .process(new ProcessWindowFunction<String, String, String, 
TimeWindow>() {
          @Override
          public void process(String s, ProcessWindowFunction<String, String, 
String, TimeWindow>.Context context,
              Iterable<String> elements, Collector<String> out) {
            for (String ele: elements) {
              out.collect(ele);
            }
          }
        }).print();
  }

  public static final class Generator implements SourceFunction<String>, 
ListCheckpointed<Integer> {

    private static final long serialVersionUID = -2819385275681175792L;

    private final int numKeys;
    private final int idlenessMs;
    private final int recordsToEmit;

    private volatile int numRecordsEmitted = 0;
    private volatile boolean canceled = false;

    Generator(final int numKeys, final int idlenessMs, final int 
durationSeconds) {
      this.numKeys = numKeys;
      this.idlenessMs = idlenessMs;

      this.recordsToEmit = ((durationSeconds * 1000) / idlenessMs) * numKeys;
    }

    @Override
    public void run(final SourceContext<String> ctx) throws Exception {
      Random rnd = new Random();
      while (numRecordsEmitted < recordsToEmit) {
        synchronized (ctx.getCheckpointLock()) {
          for (int i = 0; i < numKeys; i++) {
            ctx.collect("" + rnd.nextInt(1));
            numRecordsEmitted++;
          }
        }
        Thread.sleep(idlenessMs);
      }

      while (!canceled) {
        Thread.sleep(50);
      }

    }

    @Override
    public void cancel() {
      canceled = true;
    }

    @Override
    public List<Integer> snapshotState(final long checkpointId, final long 
timestamp) {
      return Collections.singletonList(numRecordsEmitted);
    }

    @Override
    public void restoreState(final List<Integer> states) {
      for (final Integer state : states) {
        numRecordsEmitted += state;
      }
    }
  }
}
 {code}
 

 Code to simulate flink checkpointing and timer creation and deletion and 
reproduce the problem:
{code:cpp}
//
//  main.cpp
//  reproduce
//
//  Created by shenjiaqi on 2022/2/8.
//

#include <iostream>
#include <filesystem>
#include <cstdio>
#include <cstdlib>
#include <string>

#include "rocksdb/utilities/checkpoint.h"
#include "rocksdb/db.h"
#include "rocksdb/slice.h"
#include "rocksdb/options.h"

using namespace ROCKSDB_NAMESPACE;
using ROCKSDB_NAMESPACE::DB;
using ROCKSDB_NAMESPACE::Options;
using ROCKSDB_NAMESPACE::PinnableSlice;
using ROCKSDB_NAMESPACE::ReadOptions;
using ROCKSDB_NAMESPACE::Status;
using ROCKSDB_NAMESPACE::WriteBatch;
using ROCKSDB_NAMESPACE::WriteOptions;

std::string kDBPath = "/Users/shenjiaqi/Workspace/flink/jira/data-test"; // 
need to be reconfigured

static void createCheckpoint(rocksdb::DB *db, rocksdb::Status &s) {
    std::cout << "create checkpoint" << std::endl;
    std::string chkPath = kDBPath + "-chp";
    assert(chkPath.find("/Users/shenjiaqi/Workspace/flink/jira/") >= 0); // 
just in case
    system(("rm -rf " + chkPath).data()); // use with care.
    
    Checkpoint* checkpoint_ptr;
    s = Checkpoint::Create(db, &checkpoint_ptr);
    assert(s.ok());
    
    s = checkpoint_ptr->CreateCheckpoint(chkPath);
    assert(s.ok());
}


int main() {
    DB* db;
    Options options;
    // Optimize RocksDB. This is the easiest way to get RocksDB to perform well
    options.IncreaseParallelism();
    options.OptimizeLevelStyleCompaction();
    // create the DB if it's not already present
    options.create_if_missing = true;
    options.info_log_level = DEBUG_LEVEL;
//    options.level_compaction_dynamic_level_bytes = true;

    // open DB
    Status s = DB::Open(options, kDBPath, &db);
    assert(s.ok());

    for (int i = 0; i < 1000; ++i) {

        std::string key = "key" + /* std::to_string((int)rand()); // 
*/std::to_string(i);
        std::string value = "value" + std::to_string(i);

        // Put key-value
        s = db->Put(WriteOptions(), key, value);
        assert(s.ok());

        // delete after put
        s = db->Delete(WriteOptions(), key);
        assert(s.ok());

        if (i > 0 && (i % 5) == 0) {
            createCheckpoint(db, s);
        }
    }
    
    createCheckpoint(db, s);
    return 0;
}

{code}
Many log such as: "Moving #407 to level-1 1047 bytes" can be found in LOG of 
rocksdb (not enabled in flink by default).

  was:
When using processing time window, in some workload, there will be a lot of 
small sst files(serveral KB) in rocksdb local directory and may cause "Too many 
files error".

Use rocksdb tool ldb to find out content in sst files:
 * column family of these small sst files is "processing_window-timers".
 * most sst files are in level-1.
 * records in sst files are almost kTypeDeletion.
 * creation time of sst file correspond to checkpoint interval.

These small sst files seem to be generated when flink checkpoint is triggered. 
Although all content in sst are delete tags, they are not compacted and deleted 
in rocksdb compaction because of not intersecting with each other(rocksdb 
[compaction trivial 
move|https://github.com/facebook/rocksdb/wiki/Compaction-Trivial-Move]). And 
there seems to be no chance to delete them because of small size and not 
intersect with other sst files.

 

I will attach a simple program to reproduce the problem.

 

Since timer in processing time window is generated in strictly ascending 
order(both put and delete). So If workload of job happen to generate level-0 
sst files not intersect with each other.(for example: processing window size 
much smaller than checkpoint interval, and no window content cross checkpoint 
interval or no new data in window crossing checkpoint interval). There will be 
many small sst files generated until job restored from savepoint, or 
incremental checkpoint is disabled. 

 

May be similar problem exists when user use timer in operators with same 
workload.

 

Code to reproduce the problem:
{code:java}
package org.apache.flink.jira;

import lombok.extern.slf4j.Slf4j;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.configuration.RestOptions;
import org.apache.flink.configuration.TaskManagerOptions;
import org.apache.flink.contrib.streaming.state.RocksDBStateBackend;
import org.apache.flink.streaming.api.TimeCharacteristic;
import org.apache.flink.streaming.api.checkpoint.ListCheckpointed;
import org.apache.flink.streaming.api.datastream.DataStreamSource;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.streaming.api.functions.source.SourceFunction;
import org.apache.flink.streaming.api.functions.windowing.ProcessWindowFunction;
import 
org.apache.flink.streaming.api.windowing.assigners.TumblingProcessingTimeWindows;
import org.apache.flink.streaming.api.windowing.time.Time;
import org.apache.flink.streaming.api.windowing.windows.TimeWindow;
import org.apache.flink.util.Collector;

import java.util.Collections;
import java.util.List;
import java.util.Random;

@Slf4j
public class StreamApp  {
  public static void main(String[] args) throws Exception {
    Configuration config = new Configuration();
    config.set(RestOptions.ADDRESS, "127.0.0.1");
    config.set(RestOptions.PORT, 10086);
    config.set(TaskManagerOptions.NUM_TASK_SLOTS, 6);
    new 
StreamApp().configureApp(StreamExecutionEnvironment.createLocalEnvironment(1, 
config));
  }

  public void configureApp(StreamExecutionEnvironment env) throws Exception {

    env.enableCheckpointing(20000); // 20sec

    RocksDBStateBackend rocksDBStateBackend =
        new 
RocksDBStateBackend("file:///Users/shenjiaqi/Workspace/jira/flink-51/checkpoints/",
 true); // need to be reconfigured
    
rocksDBStateBackend.setDbStoragePath("/Users/shenjiaqi/Workspace/jira/flink-51/flink/rocksdb_local_db");
 // need to be reconfigured

    env.setStateBackend(rocksDBStateBackend);
    env.getCheckpointConfig().setCheckpointTimeout(100000);
    env.getCheckpointConfig().setTolerableCheckpointFailureNumber(5);
    env.setParallelism(1);
    env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);

    env.getConfig().setTaskCancellationInterval(10000);

    for (int i = 0; i < 1; ++i) {
      createOnePipeline(env);
    }

    env.execute("StreamApp");
  }


  private void createOnePipeline(StreamExecutionEnvironment env) {
    // data source is configured so that little window cross checkpoint interval
    DataStreamSource<String> stream = env.addSource(new Generator(1, 3000, 
3600));

    stream.keyBy(x -> x)
        // make sure window size less than checkpoint interval. though 100ms is 
too small, I think increase this value can still reproduce the problem with 
longer time.
        .window(TumblingProcessingTimeWindows.of(Time.milliseconds(100)))
        .process(new ProcessWindowFunction<String, String, String, 
TimeWindow>() {
          @Override
          public void process(String s, ProcessWindowFunction<String, String, 
String, TimeWindow>.Context context,
              Iterable<String> elements, Collector<String> out) {
            for (String ele: elements) {
              out.collect(ele);
            }
          }
        }).print();
  }

  public static final class Generator implements SourceFunction<String>, 
ListCheckpointed<Integer> {

    private static final long serialVersionUID = -2819385275681175792L;

    private final int numKeys;
    private final int idlenessMs;
    private final int recordsToEmit;

    private volatile int numRecordsEmitted = 0;
    private volatile boolean canceled = false;

    Generator(final int numKeys, final int idlenessMs, final int 
durationSeconds) {
      this.numKeys = numKeys;
      this.idlenessMs = idlenessMs;

      this.recordsToEmit = ((durationSeconds * 1000) / idlenessMs) * numKeys;
    }

    @Override
    public void run(final SourceContext<String> ctx) throws Exception {
      Random rnd = new Random();
      while (numRecordsEmitted < recordsToEmit) {
        synchronized (ctx.getCheckpointLock()) {
          for (int i = 0; i < numKeys; i++) {
            ctx.collect("" + rnd.nextInt(1));
            numRecordsEmitted++;
          }
        }
        Thread.sleep(idlenessMs);
      }

      while (!canceled) {
        Thread.sleep(50);
      }

    }

    @Override
    public void cancel() {
      canceled = true;
    }

    @Override
    public List<Integer> snapshotState(final long checkpointId, final long 
timestamp) {
      return Collections.singletonList(numRecordsEmitted);
    }

    @Override
    public void restoreState(final List<Integer> states) {
      for (final Integer state : states) {
        numRecordsEmitted += state;
      }
    }
  }
}
 {code}
 

 Code to simulate flink checkpointing and timer creation and deletion and 
reproduce the problem:
{code:cpp}
//
//  main.cpp
//  reproduce
//
//  Created by shenjiaqi on 2022/2/8.
//

#include <iostream>
#include <filesystem>
#include <cstdio>
#include <cstdlib>
#include <string>

#include "rocksdb/utilities/checkpoint.h"
#include "rocksdb/db.h"
#include "rocksdb/slice.h"
#include "rocksdb/options.h"

using namespace ROCKSDB_NAMESPACE;
using ROCKSDB_NAMESPACE::DB;
using ROCKSDB_NAMESPACE::Options;
using ROCKSDB_NAMESPACE::PinnableSlice;
using ROCKSDB_NAMESPACE::ReadOptions;
using ROCKSDB_NAMESPACE::Status;
using ROCKSDB_NAMESPACE::WriteBatch;
using ROCKSDB_NAMESPACE::WriteOptions;

std::string kDBPath = "/Users/shenjiaqi/Workspace/flink/jira/data-test"; // 
need to be reconfigured

static void createCheckpoint(rocksdb::DB *db, rocksdb::Status &s) {
    std::cout << "create checkpoint" << std::endl;
    std::string chkPath = kDBPath + "-chp";
    assert(chkPath.find("/Users/shenjiaqi/Workspace/flink/jira/") >= 0); // 
just in case
    system(("rm -rf " + chkPath).data()); // use with care.
    
    Checkpoint* checkpoint_ptr;
    s = Checkpoint::Create(db, &checkpoint_ptr);
    assert(s.ok());
    
    s = checkpoint_ptr->CreateCheckpoint(chkPath);
    assert(s.ok());
}


int main() {
    DB* db;
    Options options;
    // Optimize RocksDB. This is the easiest way to get RocksDB to perform well
    options.IncreaseParallelism();
    options.OptimizeLevelStyleCompaction();
    // create the DB if it's not already present
    options.create_if_missing = true;
    options.info_log_level = DEBUG_LEVEL;
//    options.level_compaction_dynamic_level_bytes = true;

    // open DB
    Status s = DB::Open(options, kDBPath, &db);
    assert(s.ok());

    for (int i = 0; i < 1000; ++i) {

        std::string key = "key" + /* std::to_string((int)rand()); // 
*/std::to_string(i);
        std::string value = "value" + std::to_string(i);

        // Put key-value
        s = db->Put(WriteOptions(), key, value);
        assert(s.ok());

        // delete after put
        s = db->Delete(WriteOptions(), key);
        assert(s.ok());

        if (i > 0 && (i % 5) == 0) {
            createCheckpoint(db, s);
        }
    }
    
    createCheckpoint(db, s);
    return 0;
}

{code}
Many log such as: "Moving #407 to level-1 1047 bytes" can be found in LOG of 
rocksdb (not enabled in flink by default).


> Too many small sst files in rocksdb state backend when using time window 
> created in ascending order
> ---------------------------------------------------------------------------------------------------
>
>                 Key: FLINK-26050
>                 URL: https://issues.apache.org/jira/browse/FLINK-26050
>             Project: Flink
>          Issue Type: Bug
>          Components: Runtime / State Backends
>    Affects Versions: 1.10.2, 1.14.3
>            Reporter: shen
>            Priority: Major
>         Attachments: image-2022-02-09-21-22-13-920.png, 
> image-2022-02-11-10-32-14-956.png, image-2022-02-11-10-36-46-630.png, 
> image-2022-02-14-13-04-52-325.png
>
>
> When using processing or event time windows, in some workloads, there will be 
> a lot of small sst files(serveral KB) in rocksdb local directory and may 
> cause "Too many files error".
> Use rocksdb tool ldb to find out content in sst files:
>  * column family of these small sst files is "processing_window-timers".
>  * most sst files are in level-1.
>  * records in sst files are almost kTypeDeletion.
>  * creation time of sst file correspond to checkpoint interval.
> These small sst files seem to be generated when flink checkpoint is 
> triggered. Although all content in sst are delete tags, they are not 
> compacted and deleted in rocksdb compaction because of not intersecting with 
> each other(rocksdb [compaction trivial 
> move|https://github.com/facebook/rocksdb/wiki/Compaction-Trivial-Move]). And 
> there seems to be no chance to delete them because of small size and not 
> intersect with other sst files.
>  
> I will attach a simple program to reproduce the problem.
>  
> Since timer in processing time window is generated in strictly ascending 
> order(both put and delete). So If workload of job happen to generate level-0 
> sst files not intersect with each other.(for example: processing window size 
> much smaller than checkpoint interval, and no window content cross checkpoint 
> interval or no new data in window crossing checkpoint interval). There will 
> be many small sst files generated until job restored from savepoint, or 
> incremental checkpoint is disabled. 
>  
> May be similar problem exists when user use timer in operators with same 
> workload.
>  
> Code to reproduce the problem:
> {code:java}
> package org.apache.flink.jira;
> import lombok.extern.slf4j.Slf4j;
> import org.apache.flink.configuration.Configuration;
> import org.apache.flink.configuration.RestOptions;
> import org.apache.flink.configuration.TaskManagerOptions;
> import org.apache.flink.contrib.streaming.state.RocksDBStateBackend;
> import org.apache.flink.streaming.api.TimeCharacteristic;
> import org.apache.flink.streaming.api.checkpoint.ListCheckpointed;
> import org.apache.flink.streaming.api.datastream.DataStreamSource;
> import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
> import org.apache.flink.streaming.api.functions.source.SourceFunction;
> import 
> org.apache.flink.streaming.api.functions.windowing.ProcessWindowFunction;
> import 
> org.apache.flink.streaming.api.windowing.assigners.TumblingProcessingTimeWindows;
> import org.apache.flink.streaming.api.windowing.time.Time;
> import org.apache.flink.streaming.api.windowing.windows.TimeWindow;
> import org.apache.flink.util.Collector;
> import java.util.Collections;
> import java.util.List;
> import java.util.Random;
> @Slf4j
> public class StreamApp  {
>   public static void main(String[] args) throws Exception {
>     Configuration config = new Configuration();
>     config.set(RestOptions.ADDRESS, "127.0.0.1");
>     config.set(RestOptions.PORT, 10086);
>     config.set(TaskManagerOptions.NUM_TASK_SLOTS, 6);
>     new 
> StreamApp().configureApp(StreamExecutionEnvironment.createLocalEnvironment(1, 
> config));
>   }
>   public void configureApp(StreamExecutionEnvironment env) throws Exception {
>     env.enableCheckpointing(20000); // 20sec
>     RocksDBStateBackend rocksDBStateBackend =
>         new 
> RocksDBStateBackend("file:///Users/shenjiaqi/Workspace/jira/flink-51/checkpoints/",
>  true); // need to be reconfigured
>     
> rocksDBStateBackend.setDbStoragePath("/Users/shenjiaqi/Workspace/jira/flink-51/flink/rocksdb_local_db");
>  // need to be reconfigured
>     env.setStateBackend(rocksDBStateBackend);
>     env.getCheckpointConfig().setCheckpointTimeout(100000);
>     env.getCheckpointConfig().setTolerableCheckpointFailureNumber(5);
>     env.setParallelism(1);
>     env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);
>     env.getConfig().setTaskCancellationInterval(10000);
>     for (int i = 0; i < 1; ++i) {
>       createOnePipeline(env);
>     }
>     env.execute("StreamApp");
>   }
>   private void createOnePipeline(StreamExecutionEnvironment env) {
>     // data source is configured so that little window cross checkpoint 
> interval
>     DataStreamSource<String> stream = env.addSource(new Generator(1, 3000, 
> 3600));
>     stream.keyBy(x -> x)
>         // make sure window size less than checkpoint interval. though 100ms 
> is too small, I think increase this value can still reproduce the problem 
> with longer time.
>         .window(TumblingProcessingTimeWindows.of(Time.milliseconds(100)))
>         .process(new ProcessWindowFunction<String, String, String, 
> TimeWindow>() {
>           @Override
>           public void process(String s, ProcessWindowFunction<String, String, 
> String, TimeWindow>.Context context,
>               Iterable<String> elements, Collector<String> out) {
>             for (String ele: elements) {
>               out.collect(ele);
>             }
>           }
>         }).print();
>   }
>   public static final class Generator implements SourceFunction<String>, 
> ListCheckpointed<Integer> {
>     private static final long serialVersionUID = -2819385275681175792L;
>     private final int numKeys;
>     private final int idlenessMs;
>     private final int recordsToEmit;
>     private volatile int numRecordsEmitted = 0;
>     private volatile boolean canceled = false;
>     Generator(final int numKeys, final int idlenessMs, final int 
> durationSeconds) {
>       this.numKeys = numKeys;
>       this.idlenessMs = idlenessMs;
>       this.recordsToEmit = ((durationSeconds * 1000) / idlenessMs) * numKeys;
>     }
>     @Override
>     public void run(final SourceContext<String> ctx) throws Exception {
>       Random rnd = new Random();
>       while (numRecordsEmitted < recordsToEmit) {
>         synchronized (ctx.getCheckpointLock()) {
>           for (int i = 0; i < numKeys; i++) {
>             ctx.collect("" + rnd.nextInt(1));
>             numRecordsEmitted++;
>           }
>         }
>         Thread.sleep(idlenessMs);
>       }
>       while (!canceled) {
>         Thread.sleep(50);
>       }
>     }
>     @Override
>     public void cancel() {
>       canceled = true;
>     }
>     @Override
>     public List<Integer> snapshotState(final long checkpointId, final long 
> timestamp) {
>       return Collections.singletonList(numRecordsEmitted);
>     }
>     @Override
>     public void restoreState(final List<Integer> states) {
>       for (final Integer state : states) {
>         numRecordsEmitted += state;
>       }
>     }
>   }
> }
>  {code}
>  
>  Code to simulate flink checkpointing and timer creation and deletion and 
> reproduce the problem:
> {code:cpp}
> //
> //  main.cpp
> //  reproduce
> //
> //  Created by shenjiaqi on 2022/2/8.
> //
> #include <iostream>
> #include <filesystem>
> #include <cstdio>
> #include <cstdlib>
> #include <string>
> #include "rocksdb/utilities/checkpoint.h"
> #include "rocksdb/db.h"
> #include "rocksdb/slice.h"
> #include "rocksdb/options.h"
> using namespace ROCKSDB_NAMESPACE;
> using ROCKSDB_NAMESPACE::DB;
> using ROCKSDB_NAMESPACE::Options;
> using ROCKSDB_NAMESPACE::PinnableSlice;
> using ROCKSDB_NAMESPACE::ReadOptions;
> using ROCKSDB_NAMESPACE::Status;
> using ROCKSDB_NAMESPACE::WriteBatch;
> using ROCKSDB_NAMESPACE::WriteOptions;
> std::string kDBPath = "/Users/shenjiaqi/Workspace/flink/jira/data-test"; // 
> need to be reconfigured
> static void createCheckpoint(rocksdb::DB *db, rocksdb::Status &s) {
>     std::cout << "create checkpoint" << std::endl;
>     std::string chkPath = kDBPath + "-chp";
>     assert(chkPath.find("/Users/shenjiaqi/Workspace/flink/jira/") >= 0); // 
> just in case
>     system(("rm -rf " + chkPath).data()); // use with care.
>     
>     Checkpoint* checkpoint_ptr;
>     s = Checkpoint::Create(db, &checkpoint_ptr);
>     assert(s.ok());
>     
>     s = checkpoint_ptr->CreateCheckpoint(chkPath);
>     assert(s.ok());
> }
> int main() {
>     DB* db;
>     Options options;
>     // Optimize RocksDB. This is the easiest way to get RocksDB to perform 
> well
>     options.IncreaseParallelism();
>     options.OptimizeLevelStyleCompaction();
>     // create the DB if it's not already present
>     options.create_if_missing = true;
>     options.info_log_level = DEBUG_LEVEL;
> //    options.level_compaction_dynamic_level_bytes = true;
>     // open DB
>     Status s = DB::Open(options, kDBPath, &db);
>     assert(s.ok());
>     for (int i = 0; i < 1000; ++i) {
>         std::string key = "key" + /* std::to_string((int)rand()); // 
> */std::to_string(i);
>         std::string value = "value" + std::to_string(i);
>         // Put key-value
>         s = db->Put(WriteOptions(), key, value);
>         assert(s.ok());
>         // delete after put
>         s = db->Delete(WriteOptions(), key);
>         assert(s.ok());
>         if (i > 0 && (i % 5) == 0) {
>             createCheckpoint(db, s);
>         }
>     }
>     
>     createCheckpoint(db, s);
>     return 0;
> }
> {code}
> Many log such as: "Moving #407 to level-1 1047 bytes" can be found in LOG of 
> rocksdb (not enabled in flink by default).



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