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https://issues.apache.org/jira/browse/HBASE-17172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15714463#comment-15714463
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Jingcheng Du commented on HBASE-17172:
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We design the mob to reduce the IO amplification. The design tries to guarantee
the read performance no matter how many mob files there are. So we can reduce
the compacted files (which leads to too many files) by setting such a
threshold. We don't need to limit the number of files to small to fast the
reading. That is why the default threshold is small, and that is why your
compact policy JIRA is so important:)
The threshold is a key to reduce IO amplification, so we don't recommend to set
it as a very large number. Otherwise, mob doesn't have too many differences
from storing cells directly in HBase.
> Optimize major mob compaction with _del files
> ---------------------------------------------
>
> Key: HBASE-17172
> URL: https://issues.apache.org/jira/browse/HBASE-17172
> Project: HBase
> Issue Type: Improvement
> Components: mob
> Affects Versions: 2.0.0
> Reporter: huaxiang sun
> Assignee: huaxiang sun
>
> Today, when there is a _del file in mobdir, with major mob compaction, every
> mob file will be recompacted, this causes lots of IO and slow down major mob
> compaction (may take months to finish). This needs to be improved. A few
> ideas are:
> 1) Do not compact all _del files into one, instead, compact them based on
> groups with startKey as the key. Then use firstKey/startKey to make each mob
> file to see if the _del file needs to be included for this partition.
> 2). Based on the timerange of the _del file, compaction for files after that
> timerange does not need to include the _del file as these are newer files.
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