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From "jiraposter@reviews.apache.org (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2834) ByteBuffer-based read API for DFSInputStream
Date Wed, 07 Mar 2012 00:12:05 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2834?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13223847#comment-13223847
] 

jiraposter@reviews.apache.org commented on HDFS-2834:
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This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/4212/#review5665
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some stuff around error cases here -- I think you'd run into these bugs if you hit a checksum
error, since the "retry on different node" path would trigger in DFSInputStream, but the target
buffer's position would be prematurely updated from prior attempts.

But getting close!

Is it possible to split out the test refactor change from this one? Hard to tell what's changed
in the tests vs just refactored. If it's a pain in the butt I'll look more closely.


hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReader.java
<https://reviews.apache.org/r/4212/#comment12328>

    unused import?



hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocal.java
<https://reviews.apache.org/r/4212/#comment12329>

    please use javadoc style comments for these, rather than //s



hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocal.java
<https://reviews.apache.org/r/4212/#comment12330>

    I envision some silly user setting the buffer size < bytesPerChecksum and getting screwed
here. Worth a check for valid range here (throwing IOE or IllegalArgumentException or something)



hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocal.java
<https://reviews.apache.org/r/4212/#comment12331>

    This isn't your bug, but I just realized there's a potential leak here if the skip() calls
below failed. I think we need to add a try..finally{} which returns these buffers to the pool
if construction fails



hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocal.java
<https://reviews.apache.org/r/4212/#comment12332>

    should this line go in a finally{} clause? Otherwise if 'to' doesn't have enough space
for the copy, we'd end up leaving 'from' with the modified limit



hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocal.java
<https://reviews.apache.org/r/4212/#comment12333>

    in finally{} clause perhaps, so the limit isn't messed up by a failed read



hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocal.java
<https://reviews.apache.org/r/4212/#comment12337>

    the error conditions here don't quite work right.
    For example, if a checksum error occurs, the buffer's position will still be updated.
    
    Above, there's a similar problem if "phase 1" succeeds but "phase 2" encounters an error
-- the position will change but the method will throw.



hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocal.java
<https://reviews.apache.org/r/4212/#comment12338>

    no '-'s needed in javadoc



hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java
<https://reviews.apache.org/r/4212/#comment12336>

    do you really need synchronization here and below? it seems like the strategy is being
called from a synchronized context, so this is redundant. Removing this also allows the inner
classes to be static which I think is preferable



hadoop-hdfs-project/hadoop-hdfs/src/main/native/hdfs.c
<https://reviews.apache.org/r/4212/#comment12342>

    worth printing the exception message



hadoop-hdfs-project/hadoop-hdfs/src/main/native/hdfs.c
<https://reviews.apache.org/r/4212/#comment12340>

    do you need to do something here to clear the JVM exception state? you'll probably have
an OOME pending here. Probably good to use errNoFromException so that you get a reasonable
error code (assume it does something good with OOME).



hadoop-hdfs-project/hadoop-hdfs/src/main/native/hdfs.c
<https://reviews.apache.org/r/4212/#comment12343>

    is there any logging setting for libhdfs? seems like you'd want to print the stack trace
if some debug flag is set



hadoop-hdfs-project/hadoop-hdfs/src/main/native/hdfs.c
<https://reviews.apache.org/r/4212/#comment12344>

    style, } else {


- Todd


On 2012-03-06 23:14:07, Henry Robinson wrote:
bq.  
bq.  -----------------------------------------------------------
bq.  This is an automatically generated e-mail. To reply, visit:
bq.  https://reviews.apache.org/r/4212/
bq.  -----------------------------------------------------------
bq.  
bq.  (Updated 2012-03-06 23:14:07)
bq.  
bq.  
bq.  Review request for hadoop-hdfs and Todd Lipcon.
bq.  
bq.  
bq.  Summary
bq.  -------
bq.  
bq.  New patch for HDFS-2834 (I can't update the old review request).
bq.  
bq.  
bq.  This addresses bug HDFS-2834.
bq.      http://issues.apache.org/jira/browse/HDFS-2834
bq.  
bq.  
bq.  Diffs
bq.  -----
bq.  
bq.    hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReader.java
dfab730 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocal.java
cc61697 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java
4187f1c 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java
2b817ff 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/RemoteBlockReader.java
b7da8d4 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/RemoteBlockReader2.java
ea24777 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/main/native/hdfs.h 0ee29d5 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/main/native/hdfs.c 7371caf 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/BlockReaderTestUtil.java
9d4f4a2 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestParallelLocalRead.java
PRE-CREATION 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestParallelRead.java
bbd0012 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestParallelReadUtil.java
PRE-CREATION 
bq.    hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestShortCircuitLocalRead.java
eb2a1d8 
bq.  
bq.  Diff: https://reviews.apache.org/r/4212/diff
bq.  
bq.  
bq.  Testing
bq.  -------
bq.  
bq.  
bq.  Thanks,
bq.  
bq.  Henry
bq.  
bq.


                
> ByteBuffer-based read API for DFSInputStream
> --------------------------------------------
>
>                 Key: HDFS-2834
>                 URL: https://issues.apache.org/jira/browse/HDFS-2834
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Henry Robinson
>            Assignee: Henry Robinson
>         Attachments: HDFS-2834-no-common.patch, HDFS-2834.3.patch, HDFS-2834.4.patch,
HDFS-2834.5.patch, HDFS-2834.6.patch, HDFS-2834.7.patch, HDFS-2834.8.patch, HDFS-2834.patch,
HDFS-2834.patch, hdfs-2834-libhdfs-benchmark.png
>
>
> The {{DFSInputStream}} read-path always copies bytes into a JVM-allocated {{byte[]}}.
Although for many clients this is desired behaviour, in certain situations, such as native-reads
through libhdfs, this imposes an extra copy penalty since the {{byte[]}} needs to be copied
out again into a natively readable memory area. 
> For these cases, it would be preferable to allow the client to supply its own buffer,
wrapped in a {{ByteBuffer}}, to avoid that final copy overhead. 

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