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From "William Slacum (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-1801) Create a SelectColumnsIterator
Date Tue, 22 Oct 2013 16:11:44 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-1801?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13801960#comment-13801960
] 

William Slacum commented on ACCUMULO-1801:
------------------------------------------

What's the difference between this iterator and a stack that consists of a column family filter
for the projection columns + the predicate input columns, the user predicate, and a column
family filter for the projection columns?

> 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: 1.5.1, 1.6.0
>
>
> 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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