[jira] [Commented] (HBASE-5878) Use getVisibleLength public api from HdfsDataInputStream from Hadoop-2.

["Jieshan Bean (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-5878?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13263361#comment-13263361 ] 

Jieshan Bean commented on HBASE-5878:
-------------------------------------

bq.We can make use of it, when we are not able to find the getFileLength api from DFSInputStream as a else condition. So, that we will not have any sudden surprise like we are facing today.
+1 on this idea.


                
> Use getVisibleLength public api from HdfsDataInputStream from Hadoop-2.
> -----------------------------------------------------------------------
>
>                 Key: HBASE-5878
>                 URL: https://issues.apache.org/jira/browse/HBASE-5878
>             Project: HBase
>          Issue Type: Bug
>          Components: wal
>            Reporter: Uma Maheswara Rao G
>            Assignee: Uma Maheswara Rao G
>
> SequencFileLogReader: 
> Currently Hbase using getFileLength api from DFSInputStream class by reflection. DFSInputStream is not exposed as public. So, this may change in future. Now HDFS exposed HdfsDataInputStream as public API.
> We can make use of it, when we are not able to find the getFileLength api from DFSInputStream as a else condition. So, that we will not have any sudden surprise like we are facing today.
> Also,  it is just logging one warn message and proceeding if it throws any exception while getting the length. I think we can re-throw the exception because there is no point in continuing with dataloss.
> {code}
> long adjust = 0;
>           try {
>             Field fIn = FilterInputStream.class.getDeclaredField("in");
>             fIn.setAccessible(true);
>             Object realIn = fIn.get(this.in);
>             // In hadoop 0.22, DFSInputStream is a standalone class.  Before this,
>             // it was an inner class of DFSClient.
>             if (realIn.getClass().getName().endsWith("DFSInputStream")) {
>               Method getFileLength = realIn.getClass().
>                 getDeclaredMethod("getFileLength", new Class<?> []{});
>               getFileLength.setAccessible(true);
>               long realLength = ((Long)getFileLength.
>                 invoke(realIn, new Object []{})).longValue();
>               assert(realLength >= this.length);
>               adjust = realLength - this.length;
>             } else {
>               LOG.info("Input stream class: " + realIn.getClass().getName() +
>                   ", not adjusting length");
>             }
>           } catch(Exception e) {
>             SequenceFileLogReader.LOG.warn(
>               "Error while trying to get accurate file length.  " +
>               "Truncation / data loss may occur if RegionServers die.", e);
>           }
>           return adjust + super.getPos();
> {code}

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