[jira] [Commented] (HIVE-11945) ORC with non-local reads may not be reusing connection to DN

["Sergey Shelukhin (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-11945?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14906867#comment-14906867 ] 

Sergey Shelukhin commented on HIVE-11945:
-----------------------------------------

{noformat}
if (zcr != null) {
{noformat}
branch after the removed seek in RecordReaderUtils is not changed. Does it depend on this seek?

Other than that, the patch makes sense. Did you test that it fixes the issue?

> ORC with non-local reads may not be reusing connection to DN
> ------------------------------------------------------------
>
>                 Key: HIVE-11945
>                 URL: https://issues.apache.org/jira/browse/HIVE-11945
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Rajesh Balamohan
>            Assignee: Rajesh Balamohan
>         Attachments: HIVE-11945.1.patch
>
>
> When “seek + readFully(buffer, offset, length)” is used,  DFSInputStream ends up going via “readWithStrategy()”.  This sets up BlockReader with length equivalent to that of the block size. So until this position is reached, RemoteBlockReader2.peer would not be added to the PeerCache (Plz refer RemoteBlockReader2.close() in HDFS).  So eventually the next call to the same DN would end opening a new socket.  In ORC, when it is not a data local read, this has a the possibility of opening/closing lots of connections with DN.  
> In random reads, it would be good to set this length to the amount of data that is to be read (e.g pread call in DFSInputStream which sets up the BlockReader’s length correctly & the code path returns the Peer back to peer cache properly).  “readFully(position, buffer, offset, length)” follows this code path and ends up reusing the connections properly. Creating this JIRA to fix this issue.



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