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From "Josh Elser (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-1801) Create a SelectColumnsIterator
Date Tue, 10 Jun 2014 15:10:03 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-1801?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14026546#comment-14026546
] 

Josh Elser commented on ACCUMULO-1801:
--------------------------------------

Clarifying on Russ's comment (because I had to re-read it a few times), the case he is outlining
is subject only when using the RowDeletingIterator which is a special iterator that lazily
deletes an entire row using a special colfam+colqual marker (both cf and cq are empty). For
the RowDeletingIterator to see this marker, it also needs to be read from disk, which is where
his issue came from.

> Create a SelectColumnsIterator
> ------------------------------
>
>                 Key: ACCUMULO-1801
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1801
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: client
>            Reporter: Mike Drob
>            Priority: Minor
>             Fix For: 1.7.0
>
>
> A user can already limit columns on a scanner, however there is not an easy way to limit
the columns propagated in the middle of an iterator stack. For example, if a user has data
like the following:
> {noformat}
> user-1 age:25
> user-1 occupation:Student
> user-2 age:45
> user-2 occupation:Engineer
> {noformat}
> and wants to get only the users that are younger than 30, it is easy to write a custom
{{RowFilter}} to do that.
> However, to get only the occupation of users under 30, there would need to be additional
filtering done on the client side. If the rows get large or particularly numerous, then this
becomes undesirable. And setting the fetch columns is not an option since that would hide
the age column from the {{RowFilter}}.



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