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From "Keith Turner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-625) consider augmenting session state with "breadcrumbs"
Date Mon, 14 Jan 2013 17:40:13 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13552917#comment-13552917
] 

Keith Turner commented on ACCUMULO-625:
---------------------------------------

For the unique column case, I think it would be ok if the iterator considered more than a
row.  The iterator could drop any key that contains a column it has seen before.  It would
start w/ an empty set of seen columns each time its initialized. The M/R job would still need
to do the final unique.  The iterator would just do a lot of filtering.  If we supported stateful
iterators, then maybe the 100 most recently seen columns could be maintained in that state
across iterator sessions.
                
> consider augmenting session state with "breadcrumbs"
> ----------------------------------------------------
>
>                 Key: ACCUMULO-625
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-625
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: tserver
>            Reporter: Eric Newton
>            Assignee: Keith Turner
>
> Presently, the iterator stack can be created and destroyed at the whim of the tserver
and its buffering needs.  In complex iterations, lower-level iterators can make significant
progress which is not inherently obvious in any returned key.  When the iterator stack is
re-created to continue a query, the last key returned is used to {{seek()}} the iterators.
 Lower-level iterators must re-scan their data to move back to the old position.
> Consider a mechanism to save progress beyond the last key returned.
>   

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