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From "Ted Dunning (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-20) Limit Operator Reference Implementation
Date Fri, 25 Jan 2013 00:31:13 GMT

    [ https://issues.apache.org/jira/browse/DRILL-20?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13562204#comment-13562204
] 

Ted Dunning commented on DRILL-20:
----------------------------------

{quote}
 [~gera.shegalov], [~julianhyde] and [~tdunning], do any of you have any thoughts on whether
segment-based limit should be a part of the limit logical operator?
{quote}

In Dremelish settings, limit itself is rarely used at the top-level because it generally implies
a sort step.  The only exception might be debugging where you just want to see some of the
output.  Approximate top() is used almost exclusively for these sorts of situations and it
should be supported in segment and top-level contexts.

That said, I would think it useful to support top-level and per segment limit as well as top.
 One use-case that I can imagine is in recommendations where I would want to retain the first
or last records for each user, but do not want more than, say, 1000 events.  The input would
already be approximately in temporal order so limit would be fine.  It would be better, even
in this case to use top so I could specify a precise retention criterion  such as time or
a random number, but limit should be supported as well.

                
> Limit Operator Reference Implementation
> ---------------------------------------
>
>                 Key: DRILL-20
>                 URL: https://issues.apache.org/jira/browse/DRILL-20
>             Project: Apache Drill
>          Issue Type: Improvement
>            Reporter: Chris Merrick
>         Attachments: limit-reference.patch
>
>
> Build off of Jacques work on reference implementations - the limit operator.

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