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Date: Mon, 30 Jul 2012 03:07:34 +0000 (UTC)
From: "Lars Hofhansl (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=13424672#comment-13424672 ] 

Lars Hofhansl commented on HBASE-6427:
--------------------------------------

bq. This illustrates the intricacies of scanner chaining.
I think that is a false transitive statement. :)
For this particular hook chaining is hard, because this is an intricate part of the HBase code. That does not mean that chaining is generally hard (it is not).

bq. I wouldn't expect it to function correctly when an arbitrary number of scanners are chained (both) upstream and downstream.
Same here... The point is: It is possible to chain region observers even in this case.
If that is not desired an implementer can break the chain (via the passed context. and by ignoring the InternalScanner argument).

                
> 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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