Return-Path: X-Original-To: apmail-hive-dev-archive@www.apache.org Delivered-To: apmail-hive-dev-archive@www.apache.org Received: from mail.apache.org (hermes.apache.org [140.211.11.3]) by minotaur.apache.org (Postfix) with SMTP id 262B110D84 for ; Mon, 29 Apr 2013 20:48:21 +0000 (UTC) Received: (qmail 10445 invoked by uid 500); 29 Apr 2013 20:48:16 -0000 Delivered-To: apmail-hive-dev-archive@hive.apache.org Received: (qmail 10388 invoked by uid 500); 29 Apr 2013 20:48:16 -0000 Mailing-List: contact dev-help@hive.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: dev@hive.apache.org Delivered-To: mailing list dev@hive.apache.org Received: (qmail 10346 invoked by uid 500); 29 Apr 2013 20:48:16 -0000 Delivered-To: apmail-hadoop-hive-dev@hadoop.apache.org Received: (qmail 10333 invoked by uid 99); 29 Apr 2013 20:48:16 -0000 Received: from arcas.apache.org (HELO arcas.apache.org) (140.211.11.28) by apache.org (qpsmtpd/0.29) with ESMTP; Mon, 29 Apr 2013 20:48:16 +0000 Date: Mon, 29 Apr 2013 20:48:15 +0000 (UTC) From: "Shreepadma Venugopalan (JIRA)" To: hive-dev@hadoop.apache.org Message-ID: In-Reply-To: References: Subject: [jira] [Updated] (HIVE-4435) Column stats: Distinct value estimator should use hash functions that are pairwise independent MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-JIRA-FingerPrint: 30527f35849b9dde25b450d4833f0394 [ https://issues.apache.org/jira/browse/HIVE-4435?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Shreepadma Venugopalan updated HIVE-4435: ----------------------------------------- Attachment: chart_1(1).png > Column stats: Distinct value estimator should use hash functions that are pairwise independent > ---------------------------------------------------------------------------------------------- > > Key: HIVE-4435 > URL: https://issues.apache.org/jira/browse/HIVE-4435 > Project: Hive > Issue Type: Bug > Components: Statistics > Affects Versions: 0.10.0 > Reporter: Shreepadma Venugopalan > Assignee: Shreepadma Venugopalan > Attachments: chart_1(1).png, HIVE-4435.1.patch > > > The current implementation of Flajolet-Martin estimator to estimate the number of distinct values doesn't use hash functions that are pairwise independent. This is problematic because the input values don't distribute uniformly. When run on large TPC-H data sets, this leads to a huge discrepancy for primary key columns. Primary key columns are typically a monotonically increasing sequence. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira