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: vrodio...@carrieriq.com ________________________________________ From: Suraj Varma [svarma...@gmail.com] Sent: Saturday, June 22, 2013 11:51 AM To: user@hbase.apache.org 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 <pengyunm...@gmail.com> 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 < > jean-m...@spaggiari.org> 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 <pengyunm...@gmail.com>: > > > 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 < > > > jean-m...@spaggiari.org> 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 <pengyunm...@gmail.com>: > > >> > 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 > > >> > > > Confidentiality Notice: The information contained in this message, including any attachments hereto, may be confidential and is intended to be read only by the individual or entity to whom this message is addressed. If the reader of this message is not the intended recipient or an agent or designee of the intended recipient, please note that any review, use, disclosure or distribution of this message or its attachments, in any form, is strictly prohibited. If you have received this message in error, please immediately notify the sender and/or notificati...@carrieriq.com and delete or destroy any copy of this message and its attachments.
