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https://issues.apache.org/jira/browse/HDFS-6596?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14047779#comment-14047779
]
Hadoop QA commented on HDFS-6596:
---------------------------------
{color:green}+1 overall{color}. Here are the results of testing the latest
attachment
http://issues.apache.org/jira/secure/attachment/12653150/HDFS-6596.3.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:green}+1 javadoc{color}. There were no new javadoc warning messages.
{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:green}+1 core tests{color}. The patch passed unit tests in
hadoop-common-project/hadoop-common hadoop-hdfs-project/hadoop-hdfs.
{color:green}+1 contrib tests{color}. The patch passed contrib unit tests.
Test results:
https://builds.apache.org/job/PreCommit-HDFS-Build/7252//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/7252//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, HDFS-6596.2.patch,
> HDFS-6596.2.patch, HDFS-6596.3.patch, HDFS-6596.3.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.
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