Mailing-List: contact notifications-help@accumulo.apache.org; run by ezmlm
Precedence: bulk
Reply-To: jira@apache.org
Date: Sat, 29 Sep 2012 00:49:08 +1100 (NCT)
From: "Christopher Tubbs (JIRA)" <jira@apache.org>
To: notifications@accumulo.apache.org
Message-ID: <1170281096.139171.1348840148334.JavaMail.jiratomcat@arcas>
In-Reply-To: <849904581.121442.1348570567765.JavaMail.jiratomcat@arcas>
Subject: [jira] [Commented] (ACCUMULO-775) Optimize iterator seek() method
 when seeking forward
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit


    [ https://issues.apache.org/jira/browse/ACCUMULO-775?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13465604#comment-13465604 ] 

Christopher Tubbs commented on ACCUMULO-775:
--------------------------------------------

That's great, but I still see performance gains with scanning over X entries before deciding to seek, so it seems there is some room for further optimization, which we may be able to predict at a lower layer more reliably than the person writing (or the person using, in the case of a configurable iterator) the iterator that applies this scan-before-seek pattern.
                
> Optimize iterator seek() method when seeking forward
> ----------------------------------------------------
>
>                 Key: ACCUMULO-775
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-775
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: tserver
>            Reporter: Christopher Tubbs
>            Assignee: Keith Turner
>              Labels: iterator, scan, seek
>             Fix For: 1.5.0
>
>
> At present, seeking is a very expensive operation. Yet, it is a very common case, especially when writing filtering/consuming/skipping iterators to seek to the next possible match (perhaps in the next row, when matching a column family with a regular expression), rather than continuing to iterate. A common solution to the problem of whether to scan or seek is to continue to scan for some threshold (~10-20 entries), hoping to just "run into" the next possible match, rather than waste resources seeking directly to it.
> This pattern can be rolled in to the lower level iterator, so that iterators on top don't have to do this. They can seek, and the underlying source iterator can simply consume the next X entries when it makes sense, rather than waste resources seeking.
> I could be wrong (please comment and correct me below if I am), but I imagine that the places where this would make the most sense is if the data currently being sought (seek'd) is in the current compressed block from the underlying file, especially if it is forward, relative to the current pointer. A better seek method should be able to tell where one currently is, and whether the requested data is within reach without doing all the expensive operations to re-seek to the same compressed block that is already loaded, reload it, decompress it, and scan to the requested starting point.
> Having such an optimization would eliminate the need for users to try to calibrate their own such scan vs. seek optimization based on guessing whether their data is in the current block or another one, while still getting that same performance benefit.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira