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Date: Mon, 30 Jul 2012 02:16:34 +0000 (UTC)
From: "Andrew Purtell (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-6427) Pluggable compaction policies via
 coprocessors
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    [ https://issues.apache.org/jira/browse/HBASE-6427?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13424663#comment-13424663 ] 

Andrew Purtell commented on HBASE-6427:
---------------------------------------

bq. I personally haven't seen chained scanners in action. If we don't think through how chained scanners work, I wouldn't expect HBase users to use this mechanism.

Ted, this is a great comment, because I think it illustrates an incorrect approach to CP API design. (Not meant to be a criticism of you. :-)) CPs are targeted as much for HBase developers as they might be for users. The fundamental goal of CPs is to avoid needing to patch core HBase code for implementing new features or researching design alternatives. 
                
> Pluggable compaction policies via coprocessors
> ----------------------------------------------
>
>                 Key: HBASE-6427
>                 URL: https://issues.apache.org/jira/browse/HBASE-6427
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>            Priority: Minor
>         Attachments: 6427-notReady.txt, 6427-v1.txt, 6427-v2.txt, 6427-v3.txt, 6427-v4.txt, 6427-v5.txt, 6427-v7.txt
>
>
> When implementing higher level stores on top of HBase it is necessary to allow dynamic control over how long KVs must be kept around.
> Semi-static config options for ColumnFamilies (# of version or TTL) is not sufficient.
> This can be done with a few additional coprocessor hooks, or by makeing Store.ScanInfo pluggable.
> Was:
> The simplest way to achieve this is to have a pluggable class to determine the smallestReadpoint for Region. That way outside code can control what KVs to retain.

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