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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-3854) Subsequent regex subscription calls fail
Date Fri, 01 Jul 2016 18:09:11 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-3854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15359384#comment-15359384
] 

ASF GitHub Bot commented on KAFKA-3854:
---------------------------------------

GitHub user vahidhashemian reopened a pull request:

    https://github.com/apache/kafka/pull/1572

    KAFKA-3854: Fix issues with new consumer's subsequent regex (pattern) subscriptions

    This patch fixes two issues:
    1. Subsequent regex subscriptions fail with the new consumer.
    2. Subsequent regex subscriptions would not immediately refresh metadata to change the
subscription of the new consumer and trigger a rebalance.
    
    The final note on the JIRA stating that a later created topic that matches a consumer's
subscription pattern would not be assigned to the consumer upon creation seems to be as designed.
A repeat 
    `subscribe()` to the same pattern or some wait time until the next automatic metadata
refresh would handle that case.
    
    An integration test was also added to verify these issues are fixed with this PR.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/vahidhashemian/kafka KAFKA-3854

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/kafka/pull/1572.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #1572
    
----
commit 5fb472a48a0231aece798d601c3427bd058fc078
Author: Vahid Hashemian <vahidhashemian@us.ibm.com>
Date:   2016-06-16T21:19:32Z

    KAFKA-3854: Fix issues with new consumer's subsequent regex (pattern) subscriptions
    
    This patch fixes two issues:
    1. Subsequent regex subscriptions fail with the new consumer.
    2. Subsequent regex subscriptions would not actually refresh metadata and change the subscription
of the new consumer nor they would trigger a rebalance.
    
    The final note on the JIRA stating that a later created topic that matches a consumer's
subscription pattern would not be assigned to the consumer upon creation seems to be as designed.
A repeat subscribe() to the same pattern would be needed to handle that case.
    Unit tests for regex subscriptions will be handled in KAFKA-3897.

----


> Subsequent regex subscription calls fail
> ----------------------------------------
>
>                 Key: KAFKA-3854
>                 URL: https://issues.apache.org/jira/browse/KAFKA-3854
>             Project: Kafka
>          Issue Type: Bug
>          Components: consumer
>            Reporter: Vahid Hashemian
>            Assignee: Vahid Hashemian
>
> There are a couple of issues with regex subscription in the new consumer:
> h6. Subsequent Subscriptions Fail
> When consecutive calls are made to new consumer's [regex subscription|https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/clients/consumer/KafkaConsumer.java#L850],
like below: 
> {code}
> consumer.subscribe(Pattern.compile("..."), listener);
> consumer.poll(0);
> consumer.subscribe(Pattern.compile("f.."), listener);
> consumer.poll(0);
> {code}
> the second call fails with the following error:
> {code}
> Exception in thread "main" java.lang.IllegalStateException: Subscription to topics, partitions
and pattern are mutually exclusive
> 	at org.apache.kafka.clients.consumer.internals.SubscriptionState.subscribe(SubscriptionState.java:175)
> 	at org.apache.kafka.clients.consumer.KafkaConsumer.subscribe(KafkaConsumer.java:854)
> 	...
> {code}
> h6. Subsequent Subscriptions Fail to Trigger a Subscription Change and Rebalance
> Even after the code is tweaked to get around the above issue, only the first call to
regex subscription triggers an actual subscription and the subscription's rebalance listener.
The reason is the regex {{subscription}} / {{poll}} does not directly call {{changeSubscription(...)}}
in which {{needsPartitionAssignment}} is set and causes a rebalance. This method is called
only during the first regex {{subscription}} / {{poll}} when coordinator is unknown and [a
{{client.poll}} call|https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractCoordinator.java#L179]
is made which eventually leads to [a {{changeSubscription}} call|https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinator.java#L161].
The subsequent call does not reach this point because the coordinator is already known.
> It seems due to the same reason, if a consumer is subscribed to a pattern, and later
on a new topic is created that matches that pattern, the consumer does not become subscribed
it.



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