Replication also has downstream effects: it puts pressure on the available network bandwidth and disk I/O bandwidth when the cluster is loaded. john
From: Mohammad Tariq [mailto:donta...@gmail.com] Sent: Monday, July 01, 2013 6:35 PM To: user@hadoop.apache.org Subject: Re: intermediate results files I see. This difference is because of the fact that the next block of data will not be written to HDFS until the previous block was successfully written to 'all' the DNs selected for replication. This implies that higher RF means more time for the completion of a block write. Warm Regards, Tariq cloudfront.blogspot.com<http://cloudfront.blogspot.com> On Tue, Jul 2, 2013 at 4:39 AM, John Lilley <john.lil...@redpoint.net<mailto:john.lil...@redpoint.net>> wrote: I've seen some benchmarks where replication=1 runs at about 50MB/sec and replication=3 runs at about 33MB/sec, but I can't seem to find that now. John From: Mohammad Tariq [mailto:donta...@gmail.com<mailto:donta...@gmail.com>] Sent: Monday, July 01, 2013 5:03 PM To: user@hadoop.apache.org<mailto:user@hadoop.apache.org> Subject: Re: intermediate results files Hello John, IMHO, it doesn't matter. Your job will write the result just once. Replica creation is handled at the HDFS layer so it has nothing to with your job. Your job will still be writing at the same speed. Warm Regards, Tariq cloudfront.blogspot.com<http://cloudfront.blogspot.com> On Tue, Jul 2, 2013 at 4:16 AM, John Lilley <john.lil...@redpoint.net<mailto:john.lil...@redpoint.net>> wrote: If my reducers are going to create results that are temporary in nature (consumed by the next processing stage) is it recommended to use a replication factor <3 to improve performance? Thanks john
