[jira] [Commented] (HADOOP-12444) Consider implementing lazy seek in S3AInputStream

["Steve Loughran (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-12444?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14997266#comment-14997266 ] 

Steve Loughran commented on HADOOP-12444:
-----------------------------------------

I can see how this would be useful with code that did multiple seeks before a read, especially if they go forwards and then back a bit —yet still ahead of where you are now.


How did {{TestS3AContractSeek}} react to the fact that a seek past EOF doesn't trigger a failure until the next read?

> Consider implementing lazy seek in S3AInputStream
> -------------------------------------------------
>
>                 Key: HADOOP-12444
>                 URL: https://issues.apache.org/jira/browse/HADOOP-12444
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs/s3
>    Affects Versions: 2.7.1
>            Reporter: Rajesh Balamohan
>            Assignee: Rajesh Balamohan
>         Attachments: HADOOP-12444.1.patch, HADOOP-12444.WIP.patch
>
>
> - Currently, "read(long position, byte[] buffer, int offset, int length)" is not implemented in S3AInputStream (unlike DFSInputStream). So, "readFully(long position, byte[] buffer, int offset, int length)" in S3AInputStream goes through the default implementation of seek(), read(), seek() in FSInputStream. 
> - However, seek() in S3AInputStream involves re-opening of connection to S3 everytime (https://github.com/apache/hadoop/blob/trunk/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AInputStream.java#L115).  
> - It would be good to consider having a lazy seek implementation to reduce connection overheads to S3. (e.g Presto implements lazy seek. https://github.com/facebook/presto/blob/master/presto-hive/src/main/java/com/facebook/presto/hive/PrestoS3FileSystem.java#L623)



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)