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From "Christopher Tubbs (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-3510) Create mechanism to support priority based scheduling of read ahead tasks.
Date Fri, 23 Jan 2015 21:16:35 GMT


Christopher Tubbs commented on ACCUMULO-3510:

I look forward to examining the patch. Since it adds functionality, we cannot apply to a patch/bugfix
release, so please ensure your patch applies cleanly on the master branch. Also, if you are
currently working on this patch, please mark this issue as "In Progress" by clicking the "Start
Progress" button above, so we know you're working on it. Thanks!

> Create mechanism to support priority based scheduling of read ahead tasks. 
> ---------------------------------------------------------------------------
>                 Key: ACCUMULO-3510
>                 URL:
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: tserver
>    Affects Versions: 1.6.0
>            Reporter: marco polo
>            Assignee: marco polo
>            Priority: Minor
>             Fix For: 1.7.0
> I have many cases where ScanSessions will consume resources that I otherwise want shorter
running scans to utilize. In some cases, a scan may continue for hours, while a short running
scan may come in and execute quickly. As a result, I want to be able to adjust the priority
of these scan sessions. 
> I have a patch which is forthcoming, that breaks Session out of TabletServer and replaces
the queue in the readAheadThreadPool with a priority pool. The comparator I have created as
a proof of concept, which can be adjustable, reduces the priority of the oldest scan. Using
an aging technique, we guarantee execute of these older running scans based upon the previous
run time. As a result, we give preference to newer scans. If they execute quickly, older scans
will have an inherent rise in priority. If they also take a while, their priority will be
reduced and incoming scans will yet again be given a greater priority with the intent (and/or
hope ) their execution will be faster.
> Priority should be configurable based on the desired Session Comparator. 

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