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From "Sergey Shelukhin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7519) Support level compaction
Date Wed, 09 Jan 2013 02:36:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7519?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13547558#comment-13547558
] 

Sergey Shelukhin commented on HBASE-7519:
-----------------------------------------

>From the discussion today; from my understanding leveldb key ranges in different files
may overlap between levels; that means that compaction for a range must do something with
the leftover bits of the files, or keep old files for other ranges.
E.g. if I have two levels somewhere (in no particular order) - lN with [1,5), [6, 10] files
and lM with [1, 4), [4, 7), [8, 10] files, compaction for [4, 7] must include both of the
lN files, and produce some parts of them, or keep them, for the reads from other ranges. If
instead it uses the largest overlapping range to avoid only using parts of the files, all
ranges would eventually merge.
That would mean Compactor and other things also needs to change significantly (and become
pluggable?) afaisee.
                
> Support level compaction
> ------------------------
>
>                 Key: HBASE-7519
>                 URL: https://issues.apache.org/jira/browse/HBASE-7519
>             Project: HBase
>          Issue Type: New Feature
>          Components: Compaction
>            Reporter: Jimmy Xiang
>            Assignee: Jimmy Xiang
>         Attachments: level-compaction.pdf
>
>
> The level compaction algorithm may help HBase for some use cases, for example, read heavy
loads (especially, just one version is used), relative small key space updated frequently.

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