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HBase >> mail # user >> difference between major and minor compactions?


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Re: difference between major and minor compactions?
Hi Yun,

There is more differences.

The minor compactions are not remove the delete flags and the deleted
cells. It only merge the small files into a bigger one. Only the major
compaction (in 0.94) will deal with the delete cells. There is also
some more compaction mechanism coming in trunk with nice features.

Look at: https://issues.apache.org/jira/browse/HBASE-7902
https://issues.apache.org/jira/browse/HBASE-7680
https://issues.apache.org/jira/browse/HBASE-7680

Minor compactions are promoted to major compactions when the
compaction policy decide to compact all the files. If all the files
need to be merged, then we can run a major compaction which will do
the same thing as the minor one, but with the bonus of deleting the
required marked cells.

JM

2013/6/22 yun peng <[EMAIL PROTECTED]>:
> Thanks, JM
> It seems like the sole difference btwn major and minor compaction is the
> number of files (to be all or just a subset of storefiles). It mentioned
> very briefly in
> http://hbase.apache.org/book<http://hbase.apache.org/book/regions.arch.html>that
> "Sometimes a minor compaction will ... promote itself to being a major
> compaction". What does "sometime" exactly mean here? or any policy in HBase
> that allow application to specify when to promote a minor compaction to be
> a major (like user or some monitoring service can specify now is offpeak
> time?)
> Yun
>
>
>
> On Sat, Jun 22, 2013 at 8:51 AM, Jean-Marc Spaggiari <
> [EMAIL PROTECTED]> wrote:
>
>> Hi Yun,
>>
>> Few links:
>> - http://blog.cloudera.com/blog/2012/06/hbase-io-hfile-input-output/
>> => There is a small paragraph about compactions which explain when
>> they are triggered.
>> - http://hbase.apache.org/book/regions.arch.html 9.7.6.5
>>
>> You are almost right. Only thing is that HBase doesn't know when is
>> your offpeak, so a major compaction can be triggered anytime if the
>> minor is promoted to be a major one.
>>
>> JM
>>
>> 2013/6/22 yun peng <[EMAIL PROTECTED]>:
>> > Hi, All
>> >
>> > I am asking the different practices of major and minor compaction... My
>> > current understanding is that minor compaction, triggered automatically,
>> > usually run along with online query serving (but in background), so that
>> it
>> > is important to make it as lightweight as possible... to minimise
>> downtime
>> > (pause time) of online query.
>> >
>> > In contrast, the major compaction is invoked in  offpeak time and usually
>> > can be assume to have resource exclusively. It may have a different
>> > performance optimization goal...
>> >
>> > Correct me if wrong, but let me know if HBase does design different
>> > compaction mechanism this way..?
>> >
>> > Regards,
>> > Yun
>>