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https://issues.apache.org/jira/browse/UIMA-1110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12662478#action_12662478
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Eddie Epstein commented on UIMA-1110:
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This situation appears to be resolved.
1. the default prefetch value for a service input queue is 0, which results in
accurate load balancing. If there is a bandwidth problem with 0, which we have
not seen yet, it can be overridden in the deployment descriptor.
2. remote delegates now always have a [temp] reply queue on the remote broker,
and the prefetch value for these are always 1. Testing has shown a big
improvement going from 0 to 1, but little or no difference between 1 and 10.
Values larger than 1 can be problematic when reply CASes are very large.
3. the free CAS queue should always use a value of prefetch>0. We need to
confirm this is done.
> The default setting of prefetch=1 is causing problems
> -----------------------------------------------------
>
> Key: UIMA-1110
> URL: https://issues.apache.org/jira/browse/UIMA-1110
> Project: UIMA
> Issue Type: Bug
> Components: Async Scaleout
> Reporter: Eddie Epstein
> Assignee: Eddie Epstein
>
> The new JMX monitor occasionally shows idle times of many seconds for a
> scaled out remote delegate that is getting many CASes per second. Assuming
> the monitor is correct, the problem is that AMQ is not evenly distributing
> the work to all the service instances. Other recent experiences have
> demonstrated that uneven distribution is solved with prefetch=0.
> While there is some possibility that prefetch > 0 may be useful in some
> situations for remote delegates, for colocated delegates there is little
> doubt that a prefetch greater than 0 cannot help performance and can only
> screw up load balancing.
> prefetch=0 should be the default everywhere.
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