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HBase, mail # user - difference between major and minor compactions?


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RE: difference between major and minor compactions?
Vladimir Rodionov 2013-06-22, 23:23
Major compactions floods network, leaving for other operations too little space. The reason why major compaction are
so prohibitively expensive in HBase - 2 block replicas which need to be created in the cluster for every block written locally.

Best regards,
Vladimir Rodionov
Principal Platform Engineer
Carrier IQ, www.carrieriq.com
e-mail: [EMAIL PROTECTED]

________________________________________
From: Suraj Varma [[EMAIL PROTECTED]]
Sent: Saturday, June 22, 2013 11:51 AM
To: [EMAIL PROTECTED]
Subject: Re: difference between major and minor compactions?

> In contrast, the major compaction is invoked in  offpeak time and usually
> can be assume to have resource exclusively.

There is no resource exclusivity with major compactions. It is just more
resource _intensive_ because a major compaction will rewrite all the store
files to end up with a single store file per store as described in 9.7.6.5
Compaction in the hbase book.

So - it is because it is so resource _intensive_ that for large clusters
folks prefer to have a managed compaction (i.e. turn off major compaction
and run it off hours) so that it doesn't affect latencies for low latency
consumers, for instance.
--S

On Sat, Jun 22, 2013 at 7:35 AM, yun peng <[EMAIL PROTECTED]> wrote:

> I am more concerned with CompactionPolicy available that allows application
> to manipulate a bit how compaction should go... It looks like  there is
> newest API in .97 version
> *ExploringCompactionPolicy*<
> http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/regionserver/compactions/ExploringCompactionPolicy.html
> >,
> which allow application when we should have a major compaction.
>
> For stripe compaction, it is very interesting, will look into it. Thanks.
> Yun
>
>
> On Sat, Jun 22, 2013 at 9:24 AM, Jean-Marc Spaggiari <
> [EMAIL PROTECTED]> wrote:
>
> > 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.
>
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