From common-issues-return-20963-apmail-hadoop-common-issues-archive=hadoop.apache.org@hadoop.apache.org Mon Oct 3 18:09:56 2011 Return-Path: X-Original-To: apmail-hadoop-common-issues-archive@minotaur.apache.org Delivered-To: apmail-hadoop-common-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 E455691E3 for ; Mon, 3 Oct 2011 18:09:55 +0000 (UTC) Received: (qmail 48420 invoked by uid 500); 3 Oct 2011 18:09:55 -0000 Delivered-To: apmail-hadoop-common-issues-archive@hadoop.apache.org Received: (qmail 48397 invoked by uid 500); 3 Oct 2011 18:09:55 -0000 Mailing-List: contact common-issues-help@hadoop.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: common-issues@hadoop.apache.org Delivered-To: mailing list common-issues@hadoop.apache.org Received: (qmail 48389 invoked by uid 99); 3 Oct 2011 18:09:55 -0000 Received: from athena.apache.org (HELO athena.apache.org) (140.211.11.136) by apache.org (qpsmtpd/0.29) with ESMTP; Mon, 03 Oct 2011 18:09:55 +0000 X-ASF-Spam-Status: No, hits=-2000.5 required=5.0 tests=ALL_TRUSTED,RP_MATCHES_RCVD X-Spam-Check-By: apache.org Received: from [140.211.11.116] (HELO hel.zones.apache.org) (140.211.11.116) by apache.org (qpsmtpd/0.29) with ESMTP; Mon, 03 Oct 2011 18:09:54 +0000 Received: from hel.zones.apache.org (hel.zones.apache.org [140.211.11.116]) by hel.zones.apache.org (Postfix) with ESMTP id 215B32A60DD for ; Mon, 3 Oct 2011 18:09:34 +0000 (UTC) Date: Mon, 3 Oct 2011 18:09:34 +0000 (UTC) From: "Robert Joseph Evans (Commented) (JIRA)" To: common-issues@hadoop.apache.org Message-ID: <580435965.3775.1317665374139.JavaMail.tomcat@hel.zones.apache.org> In-Reply-To: <529458822.3599.1317662374080.JavaMail.tomcat@hel.zones.apache.org> Subject: [jira] [Commented] (HADOOP-7714) Add support in native libs for OS buffer cache management 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/HADOOP-7714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13119448#comment-13119448 ] Robert Joseph Evans commented on HADOOP-7714: --------------------------------------------- Why is the change across the entire datanode? And why are we trying to guess the usage pattern of the data based off of a hard coded read size of 256k? It seems to me that there are other HDFS use cases that are not random reads of < 256K, like the distributed cache or who knows what in the future with MRV2 where we want to keep the data cached in memory on the data node if possible. I would much rather see an optional parameter to the open API for flags like O_DIRECT. Then when HDFS talks to the data node it can also pass that information off to it when initiating a block read. That way the application can indicate how it expects to use the data. MAPREDCUE can say this is a streaming read where we will probably never reread the data again and it can also say this is reading a file from the distributed cache and 900 others are going to read this same file so keep it in memory if possible. > Add support in native libs for OS buffer cache management > --------------------------------------------------------- > > Key: HADOOP-7714 > URL: https://issues.apache.org/jira/browse/HADOOP-7714 > Project: Hadoop Common > Issue Type: Bug > Components: native > Affects Versions: 0.24.0 > Reporter: Todd Lipcon > Assignee: Todd Lipcon > Attachments: hadoop-7714-20s-prelim.txt > > > Especially in shared HBase/MR situations, management of the OS buffer cache is important. Currently, running a big MR job will evict all of HBase's hot data from cache, causing HBase performance to really suffer. However, caching of the MR input/output is rarely useful, since the datasets tend to be larger than cache and not re-read often enough that the cache is used. Having access to the native calls {{posix_fadvise}} and {{sync_data_range}} on platforms where they are supported would allow us to do a better job of managing this cache. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa For more information on JIRA, see: http://www.atlassian.com/software/jira