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Hadoop QA commented on HDFS-6596: --------------------------------- {color:red}-1 overall{color}. Here are the results of testing the latest attachment http://issues.apache.org/jira/secure/attachment/12652771/HDFS-6596.2.patch against trunk revision . {color:green}+1 @author{color}. The patch does not contain any @author tags. {color:green}+1 tests included{color}. The patch appears to include 1 new or modified test files. {color:green}+1 javac{color}. The applied patch does not increase the total number of javac compiler warnings. {color:red}-1 javadoc{color}. The javadoc tool appears to have generated 1 warning messages. See https://builds.apache.org/job/PreCommit-HDFS-Build/7238//artifact/trunk/patchprocess/diffJavadocWarnings.txt for details. {color:green}+1 eclipse:eclipse{color}. The patch built with eclipse:eclipse. {color:green}+1 findbugs{color}. The patch does not introduce any new Findbugs (version 1.3.9) warnings. {color:green}+1 release audit{color}. The applied patch does not increase the total number of release audit warnings. {color:red}-1 core tests{color}. The patch failed these unit tests in hadoop-common-project/hadoop-common hadoop-hdfs-project/hadoop-hdfs: org.apache.hadoop.hdfs.server.datanode.TestBlockRecovery {color:green}+1 contrib tests{color}. The patch passed contrib unit tests. Test results: https://builds.apache.org/job/PreCommit-HDFS-Build/7238//testReport/ Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/7238//console This message is automatically generated. > Improve InputStream when read spans two blocks > ---------------------------------------------- > > Key: HDFS-6596 > URL: https://issues.apache.org/jira/browse/HDFS-6596 > Project: Hadoop HDFS > Issue Type: Improvement > Components: hdfs-client > Affects Versions: 2.4.0 > Reporter: Zesheng Wu > Assignee: Zesheng Wu > Attachments: HDFS-6596.1.patch, HDFS-6596.2.patch > > > In the current implementation of DFSInputStream, read(buffer, offset, length) > is implemented as following: > {code} > int realLen = (int) Math.min(len, (blockEnd - pos + 1L)); > if (locatedBlocks.isLastBlockComplete()) { > realLen = (int) Math.min(realLen, locatedBlocks.getFileLength()); > } > int result = readBuffer(strategy, off, realLen, corruptedBlockMap); > {code} > From the above code, we can conclude that the read will return at most > (blockEnd - pos + 1) bytes. As a result, when read spans two blocks, the > caller must call read() second time to complete the request, and must wait > second time to acquire the DFSInputStream lock(read() is synchronized for > DFSInputStream). For latency sensitive applications, such as hbase, this will > result in latency pain point when they under massive race conditions. So here > we propose that we should loop internally in read() to do best effort read. > In the current implementation of pread(read(position, buffer, offset, > lenght)), it does loop internally to do best effort read. So we can refactor > to support this on normal read. -- This message was sent by Atlassian JIRA (v6.2#6252)