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https://issues.apache.org/jira/browse/HBASE-22346?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16830826#comment-16830826
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Sergey Shelukhin commented on HBASE-22346:
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[~stack] [~mbertozzi] does this make sense to you? preserves the old behavior
with low/no overhead when unset. We will probably run this for meta only on our
cluster and see how it goes.
> scanner priorities/deadline units are invalid for non-huge scanners
> -------------------------------------------------------------------
>
> Key: HBASE-22346
> URL: https://issues.apache.org/jira/browse/HBASE-22346
> Project: HBase
> Issue Type: Bug
> Reporter: Sergey Shelukhin
> Assignee: Sergey Shelukhin
> Priority: Major
>
> I was looking at using the priority (deadline) queue for scanner requests;
> what I see is that AnnotationReadingPriorityFunction, the only impl of the
> deadline function available, implements getDeadline as sqrt of the number of
> next() calls, from HBASE-10993.
> However, CallPriorityComparator.compare, its only caller, adds that
> "deadline" value to the callA.getReceiveTime() in milliseconds...
> That results in some sort of a meaningless value that I assume only make
> sense "by coincidence" for telling apart broad and specific classes of
> scanners... in practice next calls must be in the 1000s before it becomes
> meaningful vs small differences in ReceivedTime
> When there's contention from many scanners, e.g. small scanners for meta, or
> just users creating tons of scanners to the point where requests queue up,
> the actual deadline is not accounted for and the priority function itself is
> meaningless... In fact as queueing increases, it becomes worse because
> receivedtime differences grow.
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