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https://issues.apache.org/jira/browse/UIMA-1110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12626322#action_12626322
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Marshall Schor commented on UIMA-1110:
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Also, see UIMA-1059 - which was closed with won't fix, to be considered with
this Jira instead. (Issue in 1059 was to update dd2spring to disallow setting
prefetch on inner aggregates).
If we go with alternative 3, which is the one suggesting prefetch should be
associated with remote delegates, I think the current syntax for prefetch
(which is to put it as an attribute on the inputQueue element) is confusing -
since it has nothing here to do with the remote delegate's input queue.
Instead, it could be treated more like we did the additional tuning attributes
for remoteReplyQueueScaleout.
I agree the top level prefetch should not be used to set the prefetch for
everything. The prefetch for the free CAS Q for a cas multiplier = 10 is a
good example.
What about Alternative 4: setting prefetch for the top level queue via the
deployment descriptor arg, but then having the the others work as Alternative
3? As I recall, the remoteReplyQueueScaleout - which could be used to make
more threads available for reading the reply q - was thought to be an
alternative to setting the prefetch for the remote reply queue above 0.
> 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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