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From Nishant Kelkar <>
Subject Re: Optimising Map and Reduce numbers for Compressed Dataset
Date Wed, 13 Aug 2014 16:26:14 GMT
Maybe try this at the Hive terminal:

SET mapreduce.input.fileinputformat.split.maxsize=your_split_size;

Where "your_split_size" = SUM(all small file sizes) / #mappers you'd like

Thanks and Regards,

On Wed, Aug 13, 2014 at 4:00 AM, Ana Gillan <> wrote:

> Hi,
> I am currently experimenting with using Hive for a large dataset and I am
> having trouble with optimising the jobs.
> The dataset I have is quite a large number of fairly small gzipped files,
> but I am carrying out a series of transformations on it, which means that
> the size of the data being processed by the mappers and reducers is
> significantly larger than the input data. As such, a very small number of
> mappers and reducers are launched, but it takes a very long time to finish
> any job.
> Hive is using CombineFileInputFormat and I have also set
> hive.hadoop.supports.splittable.combineinputformat to true because the
> files are compressed. What other settings should I be looking at? Is there
> a way to specify the number of map tasks?
> Thanks,
> Ana

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