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Date: Thu, 18 Oct 2012 00:54:03 +0000 (UTC)
From: "Lars Hofhansl (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-6371) [89-fb] Tier based compaction
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    [ https://issues.apache.org/jira/browse/HBASE-6371?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13478543#comment-13478543 ] 

Lars Hofhansl commented on HBASE-6371:
--------------------------------------

Specifically a scenario I'd be interested in, is to keep a days (or two) worth of changes in a live HBase cluster. In extreme cases this might be lead to 1000's of versions, and scan performance of the latest version suffers significantly, *especially* after a major compaction which will cause all version of KVs to be jumbled together in the same file.
                
> [89-fb] Tier based compaction
> -----------------------------
>
>                 Key: HBASE-6371
>                 URL: https://issues.apache.org/jira/browse/HBASE-6371
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Akashnil
>            Assignee: Liyin Tang
>              Labels: noob
>
> Currently, the compaction selection is not very flexible and is not sensitive to the hotness of the data. Very old data is likely to be accessed less, and very recent data is likely to be in the block cache. Both of these considerations make it inefficient to compact these files as aggressively as other files. In some use-cases, the access-pattern is particularly obvious even though there is no way to control the compaction algorithm in those cases.
> In the new compaction selection algorithm, we plan to divide the candidate files into different levels according to oldness of the data that is present in those files. For each level, parameters like compaction ratio, minimum number of store-files in each compaction may be different. Number of levels, time-ranges, and parameters for each level will be configurable online on a per-column family basis.

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