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From Cody Koeninger <c...@koeninger.org>
Subject Re: How to recover in case user errors in streaming
Date Fri, 26 Jun 2015 15:16:18 GMT
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>
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(*new* *Function<Tuple2<String, String>, String>()* {
>
>        @Override
>
>        *public* String call(Tuple2<String, String> tuple2) {
>
>               *return* tuple2._2();
>
>        }});
>
>
>
> inputStream.foreachRDD(*new* *Function<JavaRDD<String>, Void>()* {
>
>
>
>        @Override
>
>        *public* Void call(JavaRDD<String> rdd) *throws* Exception {
>
>               *if*(!rdd.isEmpty())
>
>               {
>
> rdd.foreach(*new* *VoidFunction<String>()*{
>
> @Override
>
>                       *public* *void* call(String arg0) *throws*
> Exception {
>
> System.*out*.println("------------------------rdd----------"+arg0);
>
> Thread.*sleep*(1000);
>
>
>
> *throw* *new* Exception(" :::::::::::::::user and/or service
> exception::::::::::::::"+arg0);
>
>
>
>                       }});
>
>
>
>               }
>
>               *return* *null*;
>
>        }
>
> });
>
>
>
> *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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