Re: Checkpointing when reading from files?

[Fabian Hueske]

Hi,

The continuous file source is split into two components. 1) A split
generator that monitors a directory and generates splits when a new file is
observed, and 2) reading tasks that receive splits and read the referenced
files.

I think this is the code that generates input splits which are distributed
to reading tasks.
In PROCESS_ONCE mode, all files are listed once, splits are generated and
forwarded to the reading tasks.
At that point, the split generator can stop because it did all the work.
The reading tasks received all splits and maintain them in state.
When the job needs to recover, the split generator won't re-emit splits
because they are already checkpointed by the reader tasks.

@Padarn: There is no way to force a checkpoint from within an application.
Checkpoints are triggered by the JobManager.

Best, Fabian

2018-05-27 14:52 GMT+02:00 Padarn Wilson :

> I'm a bit confused about this too actually. I think the above would work
> as a solution if you want to continuously monitor a directory, but for a
> "PROCESS_ONCE" readFile source I don't think you will get a checkpoint
> emitted indicating the end of the stream.
>
> My understanding of this is that there can be no checkpoints created while 
> the file directory
>
> Trying to dig into the java code I found this:
>
> case PROCESS_ONCE:
>synchronized (checkpointLock) {
>
>   // the following check guarantees that if we restart
>   // after a failure and we managed to have a successful
>   // checkpoint, we will not reprocess the directory.
>
>   if (globalModificationTime == Long.MIN_VALUE) {
>  monitorDirAndForwardSplits(fileSystem, context);
>  globalModificationTime = Long.MAX_VALUE;
>   }
>   isRunning = false;
>}
>break;
>
> My understanding of this is that there can be no checkpoints created while 
> the file directory is read, and then once it is read the isRunning flat is 
> set to false, which means no new checkpoints are emitted.
>
> Is this correct? If so, is it possible to somehow force a checkpoint to be 
> emitted on the completion of the source?
>
>
>
> On Tue, May 22, 2018 at 3:24 AM Amit Jain  wrote:
>
>> Hi Alex,
>>
>> StreamingExecutionEnvironment#readFile is a helper function to create
>> file reader data streaming source. It uses
>> ContinuousFileReaderOperator and ContinuousFileMonitoringFunction
>> internally.
>>
>> As both file reader operator and monitoring function uses
>> checkpointing so is readFile [1], you can go with first approach.
>>
>> [1] https://ci.apache.org/projects/flink/flink-docs-
>> release-1.4/api/java/org/apache/flink/streaming/api/environment/
>> StreamExecutionEnvironment.html#readFile-org.apache.flink.api.common.io.
>> FileInputFormat-java.lang.String-org.apache.flink.
>> streaming.api.functions.source.FileProcessingMode-
>> long-org.apache.flink.api.common.typeinfo.TypeInformation-
>>
>>
>> --
>> Thanks,
>> Amit
>>
>>
>> On Mon, May 21, 2018 at 9:39 PM, NEKRASSOV, ALEXEI 
>> wrote:
>> > I want to add checkpointing to my program that reads from a set of
>> files in
>> > a directory. Without checkpointing I use readFile():
>> >
>> >
>> >
>> >   DataStream text = env.readFile(
>> >
>> >new TextInputFormat(new Path(inputPath)),
>> >
>> >inputPath,
>> >
>> >   inputProcessingMode,
>> >
>> >   1000);
>> >
>> >
>> >
>> > Should I use ContinuousFileMonitoringFunction /
>> ContinuousFileReaderOperator
>> > to add checkpointing? Or is there an easier way?
>> >
>> >
>> >
>> > How do I go from splits (that ContinuousFileMonitoringFunction
>> provides) to
>> > actual strings? I’m not clear how ContinuousFileReaderOperator can be
>> used.
>> >
>> >
>> >
>> >   DataStreamSource split =
>> > env.addSource(
>> >
>> >new ContinuousFileMonitoringFuncti
>> on(
>> >
>> >  new TextInputFormat(new
>> > Path(inputPath)),
>> >
>> >  inputProcessingMode,
>> >
>> >  1,
>> >
>> >  1000)
>> >
>> >   );
>> >
>> >
>> >
>> > Thanks,
>> > Alex
>>
>

Re: Checkpointing when reading from files?

[Padarn Wilson]

I'm a bit confused about this too actually. I think the above would work as
a solution if you want to continuously monitor a directory, but for a
"PROCESS_ONCE" readFile source I don't think you will get a checkpoint
emitted indicating the end of the stream.

My understanding of this is that there can be no checkpoints created
while the file directory

Trying to dig into the java code I found this:

case PROCESS_ONCE:
   synchronized (checkpointLock) {

  // the following check guarantees that if we restart
  // after a failure and we managed to have a successful
  // checkpoint, we will not reprocess the directory.

  if (globalModificationTime == Long.MIN_VALUE) {
 monitorDirAndForwardSplits(fileSystem, context);
 globalModificationTime = Long.MAX_VALUE;
  }
  isRunning = false;
   }
   break;

My understanding of this is that there can be no checkpoints created
while the file directory is read, and then once it is read the
isRunning flat is set to false, which means no new checkpoints are
emitted.

Is this correct? If so, is it possible to somehow force a checkpoint
to be emitted on the completion of the source?



On Tue, May 22, 2018 at 3:24 AM Amit Jain  wrote:

> Hi Alex,
>
> StreamingExecutionEnvironment#readFile is a helper function to create
> file reader data streaming source. It uses
> ContinuousFileReaderOperator and ContinuousFileMonitoringFunction
> internally.
>
> As both file reader operator and monitoring function uses
> checkpointing so is readFile [1], you can go with first approach.
>
> [1]
> https://ci.apache.org/projects/flink/flink-docs-release-1.4/api/java/org/apache/flink/streaming/api/environment/StreamExecutionEnvironment.html#readFile-org.apache.flink.api.common.io.FileInputFormat-java.lang.String-org.apache.flink.streaming.api.functions.source.FileProcessingMode-long-org.apache.flink.api.common.typeinfo.TypeInformation-
>
>
> --
> Thanks,
> Amit
>
>
> On Mon, May 21, 2018 at 9:39 PM, NEKRASSOV, ALEXEI  wrote:
> > I want to add checkpointing to my program that reads from a set of files
> in
> > a directory. Without checkpointing I use readFile():
> >
> >
> >
> >   DataStream text = env.readFile(
> >
> >new TextInputFormat(new Path(inputPath)),
> >
> >inputPath,
> >
> >   inputProcessingMode,
> >
> >   1000);
> >
> >
> >
> > Should I use ContinuousFileMonitoringFunction /
> ContinuousFileReaderOperator
> > to add checkpointing? Or is there an easier way?
> >
> >
> >
> > How do I go from splits (that ContinuousFileMonitoringFunction provides)
> to
> > actual strings? I’m not clear how ContinuousFileReaderOperator can be
> used.
> >
> >
> >
> >   DataStreamSource split =
> > env.addSource(
> >
> >new ContinuousFileMonitoringFunction(
> >
> >  new TextInputFormat(new
> > Path(inputPath)),
> >
> >  inputProcessingMode,
> >
> >  1,
> >
> >  1000)
> >
> >   );
> >
> >
> >
> > Thanks,
> > Alex
>

Re: Checkpointing when reading from files?

[Amit Jain]

Hi Alex,

StreamingExecutionEnvironment#readFile is a helper function to create
file reader data streaming source. It uses
ContinuousFileReaderOperator and ContinuousFileMonitoringFunction
internally.

As both file reader operator and monitoring function uses
checkpointing so is readFile [1], you can go with first approach.

[1] 
https://ci.apache.org/projects/flink/flink-docs-release-1.4/api/java/org/apache/flink/streaming/api/environment/StreamExecutionEnvironment.html#readFile-org.apache.flink.api.common.io.FileInputFormat-java.lang.String-org.apache.flink.streaming.api.functions.source.FileProcessingMode-long-org.apache.flink.api.common.typeinfo.TypeInformation-


--
Thanks,
Amit


On Mon, May 21, 2018 at 9:39 PM, NEKRASSOV, ALEXEI  wrote:
> I want to add checkpointing to my program that reads from a set of files in
> a directory. Without checkpointing I use readFile():
>
>
>
>   DataStream text = env.readFile(
>
>new TextInputFormat(new Path(inputPath)),
>
>inputPath,
>
>   inputProcessingMode,
>
>   1000);
>
>
>
> Should I use ContinuousFileMonitoringFunction / ContinuousFileReaderOperator
> to add checkpointing? Or is there an easier way?
>
>
>
> How do I go from splits (that ContinuousFileMonitoringFunction provides) to
> actual strings? I’m not clear how ContinuousFileReaderOperator can be used.
>
>
>
>   DataStreamSource split =
> env.addSource(
>
>new ContinuousFileMonitoringFunction(
>
>  new TextInputFormat(new
> Path(inputPath)),
>
>  inputProcessingMode,
>
>  1,
>
>  1000)
>
>   );
>
>
>
> Thanks,
> Alex

Checkpointing when reading from files?

[NEKRASSOV, ALEXEI]

I want to add checkpointing to my program that reads from a set of files in a 
directory. Without checkpointing I use readFile():

  DataStream text = env.readFile(
   new TextInputFormat(new Path(inputPath)),
   inputPath,
  inputProcessingMode,
  1000);

Should I use ContinuousFileMonitoringFunction / ContinuousFileReaderOperator to 
add checkpointing? Or is there an easier way?

How do I go from splits (that ContinuousFileMonitoringFunction provides) to 
actual strings? I'm not clear how ContinuousFileReaderOperator can be used.

  DataStreamSource split = env.addSource(
   new ContinuousFileMonitoringFunction(
 new TextInputFormat(new 
Path(inputPath)),
 inputProcessingMode,
 1,
 1000)
  );

Thanks,
Alex