Return-Path: X-Original-To: apmail-hadoop-common-user-archive@www.apache.org Delivered-To: apmail-hadoop-common-user-archive@www.apache.org Received: from mail.apache.org (hermes.apache.org [140.211.11.3]) by minotaur.apache.org (Postfix) with SMTP id E3F28E7A5 for ; Sat, 9 Feb 2013 00:41:31 +0000 (UTC) Received: (qmail 96594 invoked by uid 500); 9 Feb 2013 00:41:26 -0000 Delivered-To: apmail-hadoop-common-user-archive@hadoop.apache.org Received: (qmail 96446 invoked by uid 500); 9 Feb 2013 00:41:26 -0000 Mailing-List: contact user-help@hadoop.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: user@hadoop.apache.org Delivered-To: mailing list user@hadoop.apache.org Received: (qmail 96439 invoked by uid 99); 9 Feb 2013 00:41:26 -0000 Received: from athena.apache.org (HELO athena.apache.org) (140.211.11.136) by apache.org (qpsmtpd/0.29) with ESMTP; Sat, 09 Feb 2013 00:41:26 +0000 X-ASF-Spam-Status: No, hits=1.7 required=5.0 tests=FREEMAIL_ENVFROM_END_DIGIT,HTML_MESSAGE,RCVD_IN_DNSWL_LOW,SPF_PASS X-Spam-Check-By: apache.org Received-SPF: pass (athena.apache.org: domain of mehal01988@gmail.com designates 209.85.212.50 as permitted sender) Received: from [209.85.212.50] (HELO mail-vb0-f50.google.com) (209.85.212.50) by apache.org (qpsmtpd/0.29) with ESMTP; Sat, 09 Feb 2013 00:41:20 +0000 Received: by mail-vb0-f50.google.com with SMTP id ft2so2689265vbb.37 for ; Fri, 08 Feb 2013 16:40:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:x-received:date:message-id:subject:from:to :content-type; bh=iU1/pFvsKrmaLoDWVG3Q9Jq69PLk4onIhrZcuv8LvF0=; b=c14PHSf51077JaNcJOD4kFxODvayexDOYbUIQ4Hg3JBWM87TbWNUTY0MhxJFMJjSei E5cES6ZELvb+Oj8TvYapqdlPi1ktl5kg5s4xiC/3oXLCuPq4VwZi9K6d98ct+lKEAKQK RbfHYP2yknYHvfh0irSpzpqe0eQOdHB/Tn5jU60yHCvvOzPWzuel5WsaY/3AEcF/0j4e 0hMmm9t+Cz/fpRHh9P9LRNRnJZpGfuM35F6S05Yyx+9NzA1oLz8CTxEEIGgbMQq0l1PI 8kVdcn+kmlJ8tvVqKSCOfJ3PKSstMpY7YVMHBrgjhZ/PTjhEwLrK1gjFzqpjBkTiwXsA BcKg== MIME-Version: 1.0 X-Received: by 10.220.115.72 with SMTP id h8mr9093051vcq.43.1360370459308; Fri, 08 Feb 2013 16:40:59 -0800 (PST) Received: by 10.52.90.38 with HTTP; Fri, 8 Feb 2013 16:40:58 -0800 (PST) Date: Fri, 8 Feb 2013 16:40:58 -0800 Message-ID: Subject: How MapReduce selects data blocks for processing user request From: Mehal Patel To: user@hadoop.apache.org Content-Type: multipart/alternative; boundary=f46d04389455fd73f104d53fedea X-Virus-Checked: Checked by ClamAV on apache.org --f46d04389455fd73f104d53fedea Content-Type: text/plain; charset=ISO-8859-1 Hello All, I am confused over how MapReduce tasks select data blocks for processing user requests ? As data block replication replicates single data block over multiple datanodes, during job processing how uniquely data blocks are selected for processing user requests ? How does it guarantees that no same block gets chosen twice or thrice for different mapper task. Thank you -Mehal --f46d04389455fd73f104d53fedea Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hello All,

I am confused over how MapReduce tasks select= data blocks for processing user requests ?

As dat= a block replication replicates single data block over multiple datanodes, d= uring job processing how uniquely=A0
data blocks are selected for processing user requests ? How does it gu= arantees that no same block gets chosen twice or thrice=A0
for di= fferent mapper task.


Thank you

-Mehal
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