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From "Keith Turner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-4643) Allow iterators to interrupt themselves
Date Tue, 30 May 2017 18:16:04 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-4643?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16029864#comment-16029864
] 

Keith Turner commented on ACCUMULO-4643:
----------------------------------------

Whats the expected/desired behavior of this feature w.r.t. isolation?  When an iterator yields
and is later continued, will it be continued with the exact same data sources?  Or could it
be restarted with a different set of data sources (in which a compaction could have occurred
or new data was added)?

> Allow iterators to interrupt themselves
> ---------------------------------------
>
>                 Key: ACCUMULO-4643
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-4643
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: tserver
>    Affects Versions: 1.8.1, 2.0.0
>            Reporter: Ivan Bella
>            Assignee: Ivan Bella
>              Labels: features
>             Fix For: 2.0.0
>
>          Time Spent: 6h 10m
>  Remaining Estimate: 0h
>
> The idea here is to allow an iterator stack to send back a special key or throw a special
exception which will allow the tablet server to tear down the scan to be rebuilt later.  This
is to handle the case where an iterator is doing a lot of work without returning results to
avoid starving out other scans.
> There are two thoughts on how to do this:
> 1) A special "interrupt" key is returned from the getTopKey call that is detected in
the Tablet.nextBatch call, is not added to the results, but is used to add an unfinished range
and results in the remaining ranges to be deemed unfinished.
> 2) An special exception is thrown from the next or seek call that included the key of
the current position, and the same actions are taken as in 1).



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