From hdfs-issues-return-98086-apmail-hadoop-hdfs-issues-archive=hadoop.apache.org@hadoop.apache.org Wed Oct 1 18:37:36 2014 Return-Path: X-Original-To: apmail-hadoop-hdfs-issues-archive@minotaur.apache.org Delivered-To: apmail-hadoop-hdfs-issues-archive@minotaur.apache.org Received: from mail.apache.org (hermes.apache.org [140.211.11.3]) by minotaur.apache.org (Postfix) with SMTP id 21EB117A45 for ; Wed, 1 Oct 2014 18:37:36 +0000 (UTC) Received: (qmail 3082 invoked by uid 500); 1 Oct 2014 18:37:35 -0000 Delivered-To: apmail-hadoop-hdfs-issues-archive@hadoop.apache.org Received: (qmail 3023 invoked by uid 500); 1 Oct 2014 18:37:35 -0000 Mailing-List: contact hdfs-issues-help@hadoop.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: hdfs-issues@hadoop.apache.org Delivered-To: mailing list hdfs-issues@hadoop.apache.org Received: (qmail 3011 invoked by uid 99); 1 Oct 2014 18:37:35 -0000 Received: from arcas.apache.org (HELO arcas.apache.org) (140.211.11.28) by apache.org (qpsmtpd/0.29) with ESMTP; Wed, 01 Oct 2014 18:37:35 +0000 Date: Wed, 1 Oct 2014 18:37:35 +0000 (UTC) From: "Colin Patrick McCabe (JIRA)" To: hdfs-issues@hadoop.apache.org Message-ID: In-Reply-To: References: Subject: [jira] [Resolved] (HDFS-4697) short-circuit reads do not honor readahead settings 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/HDFS-4697?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Colin Patrick McCabe resolved HDFS-4697. ---------------------------------------- Resolution: Fixed Fix Version/s: 2.3.0 Short-circuit now honors {{dfs.datanode.readahead.bytes}}, since HDFS-5634. However, if you want short-circuit the full 4 MB of readahead that the datanode is doing, you'll need to set {{dfs.client.read.shortcircuit.buffer.size}} to 4 megabytes in your configuration. Its value is specified in bytes and it defaults to 1 megabyte. The tradeoff is slightly increased memory consumption. > short-circuit reads do not honor readahead settings > --------------------------------------------------- > > Key: HDFS-4697 > URL: https://issues.apache.org/jira/browse/HDFS-4697 > Project: Hadoop HDFS > Issue Type: Bug > Components: hdfs-client > Affects Versions: 2.0.3-alpha > Reporter: Colin Patrick McCabe > Assignee: Colin Patrick McCabe > Priority: Minor > Fix For: 2.3.0 > > > Neither the new nor the legacy short-circuit read implementations honor {{dfs.datanode.readahead.bytes}}. This can result in scenarios where non-short-circuit reads are faster for long reads, simply because they are doing more readahead, and SCR is not. We should do readahead in both cases if it is configured. -- This message was sent by Atlassian JIRA (v6.3.4#6332)