Return-Path: Delivered-To: apmail-hadoop-hive-dev-archive@minotaur.apache.org Received: (qmail 5744 invoked from network); 4 Mar 2009 21:38:20 -0000 Received: from hermes.apache.org (HELO mail.apache.org) (140.211.11.2) by minotaur.apache.org with SMTP; 4 Mar 2009 21:38:20 -0000 Received: (qmail 66558 invoked by uid 500); 4 Mar 2009 21:38:20 -0000 Delivered-To: apmail-hadoop-hive-dev-archive@hadoop.apache.org Received: (qmail 66544 invoked by uid 500); 4 Mar 2009 21:38:20 -0000 Mailing-List: contact hive-dev-help@hadoop.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: hive-dev@hadoop.apache.org Delivered-To: mailing list hive-dev@hadoop.apache.org Received: (qmail 66533 invoked by uid 99); 4 Mar 2009 21:38:19 -0000 Received: from athena.apache.org (HELO athena.apache.org) (140.211.11.136) by apache.org (qpsmtpd/0.29) with ESMTP; Wed, 04 Mar 2009 13:38:19 -0800 X-ASF-Spam-Status: No, hits=-2000.0 required=10.0 tests=ALL_TRUSTED X-Spam-Check-By: apache.org Received: from [140.211.11.140] (HELO brutus.apache.org) (140.211.11.140) by apache.org (qpsmtpd/0.29) with ESMTP; Wed, 04 Mar 2009 21:38:19 +0000 Received: from brutus (localhost [127.0.0.1]) by brutus.apache.org (Postfix) with ESMTP id CAF28234C4B8 for ; Wed, 4 Mar 2009 13:37:58 -0800 (PST) Message-ID: <1890627733.1236202678830.JavaMail.jira@brutus> Date: Wed, 4 Mar 2009 13:37:58 -0800 (PST) From: "Namit Jain (JIRA)" To: hive-dev@hadoop.apache.org Subject: [jira] Updated: (HIVE-223) when using map-side aggregates - perform single map-reduce group-by In-Reply-To: <1022304332.1231704299658.JavaMail.jira@brutus> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Virus-Checked: Checked by ClamAV on apache.org [ https://issues.apache.org/jira/browse/HIVE-223?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Namit Jain updated HIVE-223: ---------------------------- Status: Patch Available (was: Open) added test for disabling map aggregation at run time > when using map-side aggregates - perform single map-reduce group-by > ------------------------------------------------------------------- > > Key: HIVE-223 > URL: https://issues.apache.org/jira/browse/HIVE-223 > Project: Hadoop Hive > Issue Type: Improvement > Components: Query Processor > Reporter: Joydeep Sen Sarma > Assignee: Namit Jain > Attachments: 223.2.txt, 223.3.txt, 223.patch1.txt, hive.223.4.patch, patch.txt > > > today even when we do map side aggregates - we do multiple map-reduce jobs. however - the reason for doing multiple map-reduce group-bys (for single group-bys) was the fear of skews. When we are doing map side aggregates - skews should not exist for the most part. There can be two reason for skews: > - large number of entries for a single grouping set - map side aggregates should take care of this > - badness in hash function that sends too much stuff to one reducer - we should be able to take care of this by having good hash functions (and prime number reducer counts) > So i think we should be able to do a single stage map-reduce when doing map-side aggregates. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.