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