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From "Russ Weeks (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-1801) Create a SelectColumnsIterator
Date Tue, 15 Apr 2014 23:39:15 GMT


Russ Weeks commented on ACCUMULO-1801:

Just wanted to add a bit of unexpected behaviour that came down to this issue: when the RowDeletingIterator
is applied to a table, clients who call o.a.a.core.client.ScannerBase.fetchColumn prior to
scanning must remember to also fetch the empty column family+empty column qualifier. Otherwise,
"deleted" rows will still continue to show up until the table is compacted. Very confusing
behaviour! It makes sense once you understand what's going on but it's pretty counter-intuitive.

> Create a SelectColumnsIterator
> ------------------------------
>                 Key: ACCUMULO-1801
>                 URL:
>             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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