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Date: Wed, 17 Jul 2013 14:34:48 +0000 (UTC)
From: "Keith Turner (JIRA)" <jira@apache.org>
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Subject: [jira] [Updated] (ACCUMULO-1188) Sandbox iterators
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     [ https://issues.apache.org/jira/browse/ACCUMULO-1188?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Keith Turner updated ACCUMULO-1188:
-----------------------------------

    Attachment: ACCUMULO-1188_fig1.png

I was thinking about how this could be done and had the following thoughts :

 * A tablet should advertise different ports for reading and writing, so that reader can go directly to the process running scans.
 * The process running the scan should also contain the cache.

I attached fig 1 that shows the data flows I was thinking of.  I have also started to think that we should not pursue this approach or running compactions and scans in separate processes.

I think that if ACCUMULO-1454 is implemented, that it may solve the problem this ticket is trying to solve.  If an iterator gets stuck in an infinite loop ACCUMULO-1454 makes it possible to restart the tserver and avoid disruption.  

I am thinking the following should be done.

 * Use ACCUMULO-1345 and ACCUMULO-1454 to restart tservers with stuck compactions/scans.
 * Need to blacklist tablets that repeatedly fail ACCUMULO-1570

Is there any reason to pursue this ticket if we restart tservers and blacklist tablets? Even if we run user iterators in a separate process, we will still need to blacklist tablets and restart those separate processes. The only thing its seems to help with is avoiding walog recovery.  Are there other benefits?  


> Sandbox iterators
> -----------------
>
>                 Key: ACCUMULO-1188
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1188
>             Project: Accumulo
>          Issue Type: Bug
>            Reporter: Keith Turner
>             Fix For: 1.6.0
>
>         Attachments: ACCUMULO-1188_fig1.png
>
>
> It's possible that a user iterator can bring down a tablet server.  For example if it has an OOM or creates too many threads.  It would be nice if iterators could be sandboxed in some way.

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