Hi ashok, Thank you very much.
Regards Abhi Sent from my iPhone On Sep 26, 2012, at 1:32 PM, <ashok.sa...@wipro.com> wrote: > Hello Abhi, > Hope below information ll help you. > mapred.reduce.tasks > Default Value: -1 > Added In: 0.1 > The default number of reduce tasks per job. Typically set to a prime close to > the number of available hosts. Ignored when mapred.job.tracker is "local". > Hadoop set this to 1 by default, whereas hive uses -1 as its default value. > By setting this property to -1, Hive will automatically figure out what > should be the number of reducers. > hive.exec.reducers.bytes.per.reducer > Default Value: 1000000000 > Added In: > Size per reducer. The default is 1G, i.e if the input size is 10G, it will > use 10 reducers. > hive.exec.reducers.max > Default Value: 999 > Added In: > Max number of reducers will be used. If the one specified in the > configuration parameter mapred.reduce.tasks is negative, hive will use this > one as the max number of reducers when automatically determine number of > reducers. > > Thanks > Ashok S. > > From: Abhishek [mailto:abhishek.dod...@gmail.com] > Sent: 26 September 2012 22:27 > To: user@hive.apache.org > Cc: <user@hive.apache.org>; <bejoy...@yahoo.com> > Subject: Re: Hive configuration property > > Hi Ashok, > > Thanks for the reply, can you please tell me how many reducers should be > considered using for 1 GB of intermediate data. > > Regards > Abhi > > Sent from my iPhone > > On Sep 26, 2012, at 12:39 PM, <ashok.sa...@wipro.com> wrote: > > Yes Abshiek, > By setting below prop. You ll get better result. The no should depends on ur > data size. > > Regards > Ashok S. > > From: Bejoy KS [mailto:bejoy...@yahoo.com] > Sent: 26 September 2012 21:04 > To: user@hive.apache.org > Subject: Re: Hive configuration property > > Hi Abshiek > > Based on my experience you can always provide the number of reduce tasks > (mapred.reduce.tasks) based on the data volume your query handles. It can > yield you better performance numbers. > > Regards, > Bejoy KS > > From: Abhishek <abhishek.dod...@gmail.com> > To: "user@hive.apache.org" <user@hive.apache.org> > Cc: "user@hive.apache.org" <user@hive.apache.org> > Sent: Wednesday, September 26, 2012 7:04 PM > Subject: Re: Hive configuration property > > > > Thanks Bharath, Your points make sense.I'll try this "hive.exec.reducers.max" > property. > > Regards > Abhi > > > > Sent from my iPhone > > On Sep 26, 2012, at 9:23 AM, bharath vissapragada > <bharathvissapragada1...@gmail.com> wrote: > > > I'm no expert in hive, but here are my 2 cents. > > By default hive schedules a reducer per every 1 GB of data ( change that > value by modifying hive.exec.reducers.bytes.per.reducer ) . If your input > data is huge, there will be large number of reducers, which might be > unnecessary.( Sometimes large number of reducers slows down the job because > their number exceeds total task slots and they keep waiting for their turn. > Not to forget, the initialization overheads for each task..jvm etc.). > > Overall, I think there cannot be any optimum values for a cluster. It depends > on the type of queries, size of your inputs, size of map outputs in the jobs > (intermediate outputs ). So you can can check various values and see which > one is the best. From my experience setting "hive.exec.reducers.max" to total > number of reduce slots in your cluster gives you a decent performance since > all the reducers are completed in a single wave. (This may or maynot work for > you, worth giving a try). > > > On Wed, Sep 26, 2012 at 5:58 PM, Abhishek <abhishek.dod...@gmail.com> wrote: > > Hi all, > > I have doubt regarding below properties, is it a good practice to override > below properties in hive. > > If yes, what is the optimal values for the following properties? > > set hive.exec.reducers.bytes.per.reducer=<number> > In order to limit the maximum number of reducers: > set hive.exec.reducers.max=<number> > In order to set a constant number of reducers: > set mapred.reduce.tasks=<number> > > Regards > Abhi > > Sent from my iPhone > > > > -- > Regards, > Bharath .V > w:http://researchweb.iiit.ac.in/~bharath.v > > > The information contained in this electronic message and any attachments to > this message are intended for the exclusive use of the addressee(s) and may > contain proprietary, confidential or privileged information. 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