[jira] [Comment Edited] (AMQ-6456) Exclusive consumer may stop consuming in broker network

["james (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AMQ-6456?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15549439#comment-15549439 ] 

james edited comment on AMQ-6456 at 10/5/16 5:34 PM:
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It would seem that _somehow_ the choice of a particular consumer must be "visible" (in some form or another), otherwise the feature wouldn't work?  if different brokers came to different conclusions about which exclusive consumer is the "chosen one", then the exclusivity is lost.  in the Queue impl, it literally puts the first exclusive consumer subscription added to the Queue as the exclusive consumer on the dispatchSelector.  and the list of consumers in the queue is same list which is passed to the code that i patched in ConditionalNetworkForwardingBridge.  so, it's reasonable to conclude that the first subscription in the list is the one the Queue considers the "chosen" exclusive consumer.  (unless consumers have priorities, and then all bets might be off, but we don't use priorities).

we use activemq as an embedded library, so all configuration is programmatic, not xml.  i believe the config you are asking for is the DiscoveryNetworkConnector:

* prefetchSize = 1
* duplex = false
* messageTTL = 9999

the exclusiveSub isn't used other than for checking non-null.  the effect of the patch is that any exclusive consumers other than the first are ignored when checking for a local consumer.  so even though there _is_ a local consumer in my test scenario, since it is an exclusive consumer and is not the first in line, it is ignored.

that's a good point about this being a factory which i'm plugging in.  technically i could use my own modified subclass.  that said, it would be good if the core features worked as intended/expected without custom impls.  not to mention that the relevant problem code is not easily re-usable, so i'd have to duplicate a fair bit of code (if not the entire class).


was (Author: jahlborn):
It would seem that _somehow_ the choice of a particular consumer must be "visible" (in some form or another), otherwise the feature wouldn't work?  if different brokers came to different conclusions about which exclusive consumer is the "chosen one", then the exclusivity is lost.  in the Queue impl, it literally puts the first exclusive consumer subscription added to the Queue as the exclusive consumer on the dispatchSelector.  and the list of consumers in the queue is same list which is passed to the code that i patched in ConditionalNetworkForwardingBridge.  so, it's reasonable to conclude that the first subscription in the list is the one the Queue considers the "chosen" exclusive consumer.  (unless consumers have priorities, and then all bets might be off, but we don't use priorities).

we use activemq as an embedded library, so all configuration is programmatic, not xml.  i believe the config you are asking for is the DiscoveryNetworkConnector:

* prefetchSize = 1
* duplex = false
* messageTTL = 9999

the exclusiveSub isn't used other than for checking non-null.  the effect of the patch is that any exclusive consumers other than the first are ignored when checking for a local consumer.  so even though there _is_ a local consumer in my test scenario, since it is an exclusive consumer and is not the first in line, it is ignored.

that's a good point about this being a factory which i'm plugging in.  technically i could use my own modified subclass.  that said, it would be good if the core features worked as intended/expected without custom impls.

> Exclusive consumer may stop consuming in broker network
> -------------------------------------------------------
>
>                 Key: AMQ-6456
>                 URL: https://issues.apache.org/jira/browse/AMQ-6456
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.9.1, 5.14.1
>            Reporter: james
>            Priority: Critical
>         Attachments: exclusive_consumer_patch.txt
>
>
> When exclusive consumers are restarted in a network of brokers, the "chosen" consumer may shift from one broker to the next.  In order for existing messages to be consumed, they must be forwarded from the broker on which they currently exist to the broker on which the chosen consumer now resides.  However, the ConditionalNetworkBridgeFilter incorrectly decides that it should not forward the messages and they end up getting stuck on the old broker.
> We found the issue in 5.9.1, but the relevant code looks unchanged in the current 5.x release.



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