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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3110) libhdfs implementation of direct read API
Date Tue, 03 Apr 2012 23:24:23 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13245878#comment-13245878
] 

Todd Lipcon commented on HDFS-3110:
-----------------------------------

Sorry, a few things I missed when I looked at the earlier rev:

- we no longer need to expose the hdfsReadDirect API in hdfs.h, given it's automatically handled.
Instead we should probably rename to {{readDirect}} and make it static in hdfs.c. If you need
it for the test case, then I think we should just add it as an extern declaration in the test,
and leave it non-static -- but not advertise it in hdfs.h. We don't want users to think they
have to use it explicitly.


----
{code}
+    // Bit fields for  hdfsFile_internal flags
{code}
nit: extra space

----

Looks like handleReadResult returns -1 when the underlying code calls an exception. Then we
have the following code:
{code}
+    if (noReadBytes != 0) {
+      (*env)->GetByteArrayRegion(env, jbRarray, 0, noReadBytes, buffer);
     }
{code}
won't that end up calling {{GetByteArrayRegion}} with a negative length? Seems suspicious.

                
> libhdfs implementation of direct read API
> -----------------------------------------
>
>                 Key: HDFS-3110
>                 URL: https://issues.apache.org/jira/browse/HDFS-3110
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: libhdfs
>            Reporter: Henry Robinson
>            Assignee: Henry Robinson
>             Fix For: 0.24.0
>
>         Attachments: HDFS-3110.0.patch, HDFS-3110.1.patch, HDFS-3110.2.patch, HDFS-3110.3.patch
>
>
> Once HDFS-2834 gets committed, we can add support for the new API to libhdfs, which leads
to significant performance increases when reading local data from C.

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