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From Amit Assudani <aassud...@impetus.com>
Subject Re: How to recover in case user errors in streaming
Date Wed, 01 Jul 2015 17:35:45 GMT
Hi TD,

Why don’t we have OnBatchError or similar method in StreamingListener ?

Also, is StreamingListener only for receiver based approach or does it work for Kafka Direct
API / File Based Streaming as well ?

Regards,
Amit

From: Tathagata Das <tdas@databricks.com<mailto:tdas@databricks.com>>
Date: Monday, June 29, 2015 at 5:24 PM
To: amit assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
Cc: Cody Koeninger <cody@koeninger.org<mailto:cody@koeninger.org>>, "user@spark.apache.org<mailto:user@spark.apache.org>"
<user@spark.apache.org<mailto:user@spark.apache.org>>
Subject: Re: How to recover in case user errors in streaming

I recommend writing using dstream.foreachRDD, and then rdd.saveAsNewAPIHadoopFile inside try
catch. See the implementation of dstream.saveAsNewAPIHadoopFiles

https://github.com/apache/spark/blob/master/streaming/src/main/scala/org/apache/spark/streaming/dstream/PairDStreamFunctions.scala#L716

On Mon, Jun 29, 2015 at 8:44 AM, Amit Assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
wrote:
Also, how do you suggest catching exceptions while using with connector API like, saveAsNewAPIHadoopFiles
?

From: amit assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
Date: Monday, June 29, 2015 at 9:55 AM
To: Tathagata Das <tdas@databricks.com<mailto:tdas@databricks.com>>

Cc: Cody Koeninger <cody@koeninger.org<mailto:cody@koeninger.org>>, "user@spark.apache.org<mailto:user@spark.apache.org>"
<user@spark.apache.org<mailto:user@spark.apache.org>>
Subject: Re: How to recover in case user errors in streaming

Thanks TD, this helps.

Looking forward to some fix where framework handles the batch failures by some callback methods.
This will help not having to write try/catch in every transformation / action.

Regards,
Amit

From: Tathagata Das <tdas@databricks.com<mailto:tdas@databricks.com>>
Date: Saturday, June 27, 2015 at 5:14 AM
To: amit assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
Cc: Cody Koeninger <cody@koeninger.org<mailto:cody@koeninger.org>>, "user@spark.apache.org<mailto:user@spark.apache.org>"
<user@spark.apache.org<mailto:user@spark.apache.org>>
Subject: Re: How to recover in case user errors in streaming

I looked at the code and found that batch exceptions are indeed ignored. This is something
that is worth fixing, that batch exceptions should not be silently ignored.

Also, you can catch failed batch jobs (irrespective of the number of retries) by catch the
exception in foreachRDD. Here is an example.

dstream.foreachRDD { rdd =>

   try {

   } catch {

   }
}


This will catch failures at the granularity of the job, after all the max retries of a task
has been done. But it will be hard to filter and find the push the failed record(s) somewhere.
To do that, I would do use rdd.foreach or rdd.foreachPartition, inside which I would catch
the exception and push that record out to another Kafka topic, and continue normal processing
of other records. This would prevent the task process the partition from failing (as you are
catching the bad records).

dstream.foreachRDD {  rdd =>

    rdd.foreachPartition { iterator =>

         // Create Kafka producer for bad records

        iterator.foreach { record =>
             try {
                 // process record
             } catch {
                case ExpectedException =>
                    // publish bad record to error topic in Kafka using above producer
             }
        }
    }
}


TD

PS: Apologies for the Scala examples, hope you get the idea :)

On Fri, Jun 26, 2015 at 9:56 AM, Amit Assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
wrote:
Also, I get TaskContext.get() null when used in foreach function below ( I get it when I use
it in map, but the whole point here is to handle something that is breaking in action ). Please
help. :(

From: amit assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
Date: Friday, June 26, 2015 at 11:41 AM

To: Cody Koeninger <cody@koeninger.org<mailto:cody@koeninger.org>>
Cc: "user@spark.apache.org<mailto:user@spark.apache.org>" <user@spark.apache.org<mailto:user@spark.apache.org>>,
Tathagata Das <tdas@databricks.com<mailto:tdas@databricks.com>>
Subject: Re: How to recover in case user errors in streaming

Hmm, not sure why, but when I run this code, it always keeps on consuming from Kafka and proceeds
ignoring the previous failed batches,

Also, Now that I get the attempt number from TaskContext and I have information of max retries,
I am supposed to handle it in the try/catch block, but does it mean I’ve to handle these
kind of exceptions / errors in every transformation step ( map, reduce, transform, etc. ),
isn’t there any callback where it says it has been retried max number of times and before
being ignored you’ve a handle to do whatever you want to do with the batch / message in
hand.

Regards,
Amit

From: Cody Koeninger <cody@koeninger.org<mailto:cody@koeninger.org>>
Date: Friday, June 26, 2015 at 11:32 AM
To: amit assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
Cc: "user@spark.apache.org<mailto:user@spark.apache.org>" <user@spark.apache.org<mailto:user@spark.apache.org>>,
Tathagata Das <tdas@databricks.com<mailto:tdas@databricks.com>>
Subject: Re: How to recover in case user errors in streaming

No, if you have a bad message that you are continually throwing exceptions on, your stream
will not progress to future batches.

On Fri, Jun 26, 2015 at 10:28 AM, Amit Assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
wrote:
Also, what I understand is, max failures doesn’t stop the entire stream, it fails the job
created for the specific batch, but the subsequent batches still proceed, isn’t it right
? And question still remains, how to keep track of those failed batches ?

From: amit assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
Date: Friday, June 26, 2015 at 11:21 AM
To: Cody Koeninger <cody@koeninger.org<mailto:cody@koeninger.org>>

Cc: "user@spark.apache.org<mailto:user@spark.apache.org>" <user@spark.apache.org<mailto:user@spark.apache.org>>,
Tathagata Das <tdas@databricks.com<mailto:tdas@databricks.com>>
Subject: Re: How to recover in case user errors in streaming

Thanks for quick response,

My question here is how do I know that the max retries are done ( because in my code I never
know whether it is failure of first try or the last try ) and I need to handle this message,
is there any callback ?

Also, I know the limitation of checkpoint in upgrading the code, but my main focus here to
mitigate the connectivity issues to persistent store which gets resolved in a while, but how
do I know which all messages failed and need rework ?

Regards,
Amit

From: Cody Koeninger <cody@koeninger.org<mailto:cody@koeninger.org>>
Date: Friday, June 26, 2015 at 11:16 AM
To: amit assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
Cc: "user@spark.apache.org<mailto:user@spark.apache.org>" <user@spark.apache.org<mailto:user@spark.apache.org>>,
Tathagata Das <tdas@databricks.com<mailto:tdas@databricks.com>>
Subject: Re: How to recover in case user errors in streaming

If you're consistently throwing exceptions and thus failing tasks, once you reach max failures
the whole stream will stop.

It's up to you to either catch those exceptions, or restart your stream appropriately once
it stops.

Keep in mind that if you're relying on checkpoints, and fixing the error requires changing
your code, you may not be able to recover the checkpoint.

On Fri, Jun 26, 2015 at 9:05 AM, Amit Assudani <aassudani@impetus.com<mailto:aassudani@impetus.com>>
wrote:
Problem: how do we recover from user errors (connectivity issues / storage service down /
etc.)?
Environment: Spark streaming using Kafka Direct Streams
Code Snippet:

HashSet<String> topicsSet = new HashSet<String>(Arrays.asList("kafkaTopic1"));
HashMap<String, String> kafkaParams = new HashMap<String, String>();
kafkaParams.put("metadata.broker.list", "localhost:9092");
kafkaParams.put("auto.offset.reset", "smallest");


JavaPairInputDStream<String, String> messages = KafkaUtils
.createDirectStream(jssc, String.class, String.class, StringDecoder.class, StringDecoder.class,
kafkaParams, topicsSet);

JavaDStream<String> inputStream = messages
       .map(newFunction<Tuple2<String, String>, String>() {
       @Override
       public String call(Tuple2<String, String> tuple2) {
              returntuple2._2();
       }});

inputStream.foreachRDD(newFunction<JavaRDD<String>, Void>() {

       @Override
       public Void call(JavaRDD<String> rdd)throws Exception {
              if(!rdd.isEmpty())
              {
rdd.foreach(newVoidFunction<String>(){
@Override
                      publicvoid call(String arg0)throws Exception {
System.out.println("------------------------rdd----------"+arg0);
Thread.sleep(1000);

thrownew Exception(" :::::::::::::::user and/or service exception::::::::::::::"+arg0);

                      }});

              }
              returnnull;
       }
});

Detailed Description: Using spark streaming I read the text messages from kafka using direct
API. For sake of simplicity, all I do in processing is printing each message on console and
sleep of 1 sec. as a placeholder for actual processing. Assuming we get a user error may be
due to bad record, format error or the service connectivity issues or let’s say the persistent
store downtime. I’ve represented that with throwing an Exception from foreach block. I understand
spark retries this configurable number of times and  proceeds ahead. The question is what
happens to those failed messages, does ( if yes when ) spark re-tries those ? If not, does
it have any callback method so as user can log / dump it in error queue and provision it for
further analysis and / or retrials manually. Also, fyi, checkpoints are enabled and above
code is in create context method to recover from spark driver / worker failures.

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otherwise protected by law. The message is intended solely for the named addressee. If received
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