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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-3231) Handle Kinesis-side resharding in Kinesis streaming consumer
Date Tue, 28 Jun 2016 04:40:57 GMT

    [ https://issues.apache.org/jira/browse/FLINK-3231?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15352343#comment-15352343
] 

ASF GitHub Bot commented on FLINK-3231:
---------------------------------------

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

    https://github.com/apache/flink/pull/2131#discussion_r68696712
  
    --- Diff: flink-streaming-connectors/flink-connector-kinesis/src/main/java/org/apache/flink/streaming/connectors/kinesis/proxy/KinesisProxy.java
---
    @@ -86,32 +144,25 @@ public KinesisProxy(Properties configProps) {
     	 * @param maxRecordsToGet the maximum amount of records to retrieve for this batch
     	 * @return the batch of retrieved records
     	 */
    -	public GetRecordsResult getRecords(String shardIterator, int maxRecordsToGet) {
    +	@Override
    +	public GetRecordsResult getRecords(String shardIterator, int maxRecordsToGet) throws
InterruptedException {
     		final GetRecordsRequest getRecordsRequest = new GetRecordsRequest();
     		getRecordsRequest.setShardIterator(shardIterator);
     		getRecordsRequest.setLimit(maxRecordsToGet);
     
     		GetRecordsResult getRecordsResult = null;
     
    -		int remainingRetryTimes = Integer.valueOf(
    -			configProps.getProperty(KinesisConfigConstants.CONFIG_STREAM_DESCRIBE_RETRIES, Integer.toString(KinesisConfigConstants.DEFAULT_STREAM_DESCRIBE_RETRY_TIMES)));
    -		long describeStreamBackoffTimeInMillis = Long.valueOf(
    -			configProps.getProperty(KinesisConfigConstants.CONFIG_STREAM_DESCRIBE_BACKOFF, Long.toString(KinesisConfigConstants.DEFAULT_STREAM_DESCRIBE_BACKOFF)));
    -
    -		int i=0;
    -		while (i <= remainingRetryTimes && getRecordsResult == null) {
    +		int attempt = 0;
    +		while (attempt <= getRecordsMaxAttempts && getRecordsResult == null) {
     			try {
     				getRecordsResult = kinesisClient.getRecords(getRecordsRequest);
     			} catch (ProvisionedThroughputExceededException ex) {
    +				long backoffMillis = fullJitterBackoff(
    +					getRecordsBaseBackoffMillis, getRecordsMaxBackoffMillis, getRecordsExpConstant,
attempt++);
     				LOG.warn("Got ProvisionedThroughputExceededException. Backing off for "
    -					+ describeStreamBackoffTimeInMillis + " millis.");
    -				try {
    -					Thread.sleep(describeStreamBackoffTimeInMillis);
    -				} catch (InterruptedException interruptEx) {
    -					//
    -				}
    +					+ backoffMillis + " millis.");
    +				Thread.sleep(backoffMillis);
     			}
    -			i++;
     		}
     
     		if (getRecordsResult == null) {
    --- End diff --
    
    Misunderstanding here.
    The `getRecordsResult` will only be `null` here if we fail to get any response from Kinesis
due to `ProvisionedThroughputExceededException` even after 3 retries (default setting of `KinesisConfigConstants.DEFAULT_SHARD_GETRECORDS_RETRIES`).
We'll always get a `GetRecordsResult` regardless of the status of the shard.
    
    What the javadoc is saying is that if we reached the end of a shard (the shard is closed)
`GetRecordsResult#getNextShardIterator()` will return a `null`, meaning that we won't be able
to continue consuming the shard. In `ShardConsumer`, we always renew the `nextShardIterator`
with the value returned in `GetRecordsResult`. If we get a `null`, we know the shard is closed
and terminate the `ShardConsumer` thread. So, no more `getRecords()` calls will be made to
the shard after it is closed.


> Handle Kinesis-side resharding in Kinesis streaming consumer
> ------------------------------------------------------------
>
>                 Key: FLINK-3231
>                 URL: https://issues.apache.org/jira/browse/FLINK-3231
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Kinesis Connector, Streaming Connectors
>    Affects Versions: 1.1.0
>            Reporter: Tzu-Li (Gordon) Tai
>            Assignee: Tzu-Li (Gordon) Tai
>             Fix For: 1.1.0
>
>
> A big difference between Kinesis shards and Kafka partitions is that Kinesis users can
choose to "merge" and "split" shards at any time for adjustable stream throughput capacity.
This article explains this quite clearly: https://brandur.org/kinesis-by-example.
> This will break the static shard-to-task mapping implemented in the basic version of
the Kinesis consumer (https://issues.apache.org/jira/browse/FLINK-3229). The static shard-to-task
mapping is done in a simple round-robin-like distribution which can be locally determined
at each Flink consumer task (Flink Kafka consumer does this too).
> To handle Kinesis resharding, we will need some way to let the Flink consumer tasks coordinate
which shards they are currently handling, and allow the tasks to ask the coordinator for a
shards reassignment when the task finds out it has found a closed shard at runtime (shards
will be closed by Kinesis when it is merged and split).
> We need a centralized coordinator state store which is visible to all Flink consumer
tasks. Tasks can use this state store to locally determine what shards it can be reassigned.
Amazon KCL uses a DynamoDB table for the coordination, but as described in https://issues.apache.org/jira/browse/FLINK-3211,
we unfortunately can't use KCL for the implementation of the consumer if we want to leverage
Flink's checkpointing mechanics. For our own implementation, Zookeeper can be used for this
state store, but that means it would require the user to set up ZK to work.
> Since this feature introduces extensive work, it is opened as a separate sub-task from
the basic implementation https://issues.apache.org/jira/browse/FLINK-3229.



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