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https://issues.apache.org/jira/browse/HDFS-4710?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13843780#comment-13843780
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Hadoop QA commented on HDFS-4710:
---------------------------------
{color:red}-1 overall{color}. Here are the results of testing the latest
attachment
http://issues.apache.org/jira/secure/attachment/12589940/HDFS-4710.002.patch
against trunk revision .
{color:red}-1 patch{color}. The patch command could not apply the patch.
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/5682//console
This message is automatically generated.
> SCR should honor dfs.client.read.shortcircuit.buffer.size even when checksums
> are off
> -------------------------------------------------------------------------------------
>
> Key: HDFS-4710
> URL: https://issues.apache.org/jira/browse/HDFS-4710
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs-client
> Affects Versions: 2.0.4-alpha
> Environment: Centos (EC2) + short-circuit reads on
> Reporter: Gopal V
> Assignee: Colin Patrick McCabe
> Priority: Minor
> Labels: perfomance
> Attachments: HDFS-4710.001.patch, HDFS-4710.002.patch
>
>
> When short-circuit reads are on, HDFS client slows down when checksums are
> turned off.
> With checksums on, the query takes 45.341 seconds and with it turned off, it
> takes 56.345 seconds. This is slower than the speeds observed when
> short-circuiting is turned off.
> The issue seems to be that FSDataInputStream.readByte() calls are directly
> transferred to the disk fd when the checksums are turned off.
> Even though all the columns are integers, the data being read will be read
> via DataInputStream which does
> {code}
> public final int readInt() throws IOException {
> int ch1 = in.read();
> int ch2 = in.read();
> int ch3 = in.read();
> int ch4 = in.read();
> {code}
> To confirm, an strace of the Yarn container shows
> {code}
> 26690 read(154, "B", 1) = 1
> 26690 read(154, "\250", 1) = 1
> 26690 read(154, ".", 1) = 1
> 26690 read(154, "\24", 1) = 1
> {code}
> To emulate this without the entirety of Hive code, I have written a simpler
> test app
> https://github.com/t3rmin4t0r/shortcircuit-reader
> The jar will read a file in -bs <n> sized buffers. Running it with 1 byte
> blocks gives similar results to the Hive test run.
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