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 0440418C95 for ; Tue, 29 Sep 2015 08:51:06 +0000 (UTC) Received: (qmail 81514 invoked by uid 500); 29 Sep 2015 08:51:05 -0000 Delivered-To: apmail-hadoop-hdfs-issues-archive@hadoop.apache.org Received: (qmail 81455 invoked by uid 500); 29 Sep 2015 08:51:05 -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 81438 invoked by uid 99); 29 Sep 2015 08:51:05 -0000 Received: from arcas.apache.org (HELO arcas.apache.org) (140.211.11.28) by apache.org (qpsmtpd/0.29) with ESMTP; Tue, 29 Sep 2015 08:51:05 +0000 Date: Tue, 29 Sep 2015 08:51:05 +0000 (UTC) From: "Yi Liu (JIRA)" To: hdfs-issues@hadoop.apache.org Message-ID: In-Reply-To: References: Subject: [jira] [Updated] (HDFS-8859) Improve DataNode ReplicaMap memory footprint to save about 45% 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-8859?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Yi Liu updated HDFS-8859: ------------------------- Resolution: Fixed Hadoop Flags: Reviewed Fix Version/s: 2.8.0 Status: Resolved (was: Patch Available) > Improve DataNode ReplicaMap memory footprint to save about 45% > -------------------------------------------------------------- > > Key: HDFS-8859 > URL: https://issues.apache.org/jira/browse/HDFS-8859 > Project: Hadoop HDFS > Issue Type: Improvement > Components: datanode > Reporter: Yi Liu > Assignee: Yi Liu > Fix For: 2.8.0 > > Attachments: HDFS-8859.001.patch, HDFS-8859.002.patch, HDFS-8859.003.patch, HDFS-8859.004.patch, HDFS-8859.005.patch, HDFS-8859.006.patch > > > By using following approach we can save about *45%* memory footprint for each block replica in DataNode memory (This JIRA only talks about *ReplicaMap* in DataNode), the details are: > In ReplicaMap, > {code} > private final Map> map = > new HashMap>(); > {code} > Currently we use a HashMap {{Map}} to store the replicas in memory. The key is block id of the block replica which is already included in {{ReplicaInfo}}, so this memory can be saved. Also HashMap Entry has a object overhead. We can implement a lightweight Set which is similar to {{LightWeightGSet}}, but not a fixed size ({{LightWeightGSet}} uses fix size for the entries array, usually it's a big value, an example is {{BlocksMap}}, this can avoid full gc since no need to resize), also we should be able to get Element through key. > Following is comparison of memory footprint If we implement a lightweight set as described: > We can save: > {noformat} > SIZE (bytes) ITEM > 20 The Key: Long (12 bytes object overhead + 8 bytes long) > 12 HashMap Entry object overhead > 4 reference to the key in Entry > 4 reference to the value in Entry > 4 hash in Entry > {noformat} > Total: -44 bytes > We need to add: > {noformat} > SIZE (bytes) ITEM > 4 a reference to next element in ReplicaInfo > {noformat} > Total: +4 bytes > So totally we can save 40bytes for each block replica > And currently one finalized replica needs around 46 bytes (notice: we ignore memory alignment here). > We can save 1 - (4 + 46) / (44 + 46) = *45%* memory for each block replica in DataNode. > -- This message was sent by Atlassian JIRA (v6.3.4#6332)