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From "Abdullah Alamoudi (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-6607) DFSInputStream Seek performance improvement
Date Mon, 30 Jun 2014 11:00:26 GMT

     [ https://issues.apache.org/jira/browse/HDFS-6607?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Abdullah Alamoudi updated HDFS-6607:
------------------------------------

    Description: 
When having a DFSInputStream open and seeking to a position that resides in the same block,
if the target position is in the TCP buffer already, the seek is performed efficiently simply
by eating up the intervening data. See line 1368 in the file: hadoop-common/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java.

However, if the position is in the same block but after the TCP buffer, the inputstream performs
a set of actions including closing the current block reader, locating the block again, selecting
a data node and creating a new block reader. During this, many objects are created and all
of this is very inefficient for users with random access needs (e.g index access).

I have conducted some experiments which showed that reading 3,000,000 records using seeks
and reads is slower than reading 60,000,000 records using seeks and reads as well which shows
the need to improve the seek implementation.

  was:
When having a DFSInputStream open and seeking to a position that resides in the same block,
if the target position is in the TCP buffer already, the seek is performed efficiently simply
by eating up the intervening data. See line 1368 in the file: hadoop-common/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java.

However, if the position is in the same block but after the TCP buffer, the inputstream performs
a set of actions including closing the current block reader, locating the block again, selecting
a data node and creating a new block reader. During this, many objects are created and all
of this is very inefficient for users with random access needs (e.g index access).


> DFSInputStream Seek performance improvement
> -------------------------------------------
>
>                 Key: HDFS-6607
>                 URL: https://issues.apache.org/jira/browse/HDFS-6607
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client, performance
>    Affects Versions: 2.4.1
>            Reporter: Abdullah Alamoudi
>
> When having a DFSInputStream open and seeking to a position that resides in the same
block, if the target position is in the TCP buffer already, the seek is performed efficiently
simply by eating up the intervening data. See line 1368 in the file: hadoop-common/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java.
> However, if the position is in the same block but after the TCP buffer, the inputstream
performs a set of actions including closing the current block reader, locating the block again,
selecting a data node and creating a new block reader. During this, many objects are created
and all of this is very inefficient for users with random access needs (e.g index access).
> I have conducted some experiments which showed that reading 3,000,000 records using seeks
and reads is slower than reading 60,000,000 records using seeks and reads as well which shows
the need to improve the seek implementation.



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