[jira] Reopened: (HBASE-2180) Bad random read performance from synchronizing hfile.fddatainputstream

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

     [ https://issues.apache.org/jira/browse/HBASE-2180?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

stack reopened HBASE-2180:
--------------------------


Reopening to take a look.

I have a vague recollection of stuff not being closed down if not all is read out of the socket.  Thanks for reporting this Erik.

> Bad random read performance from synchronizing hfile.fddatainputstream
> ----------------------------------------------------------------------
>
>                 Key: HBASE-2180
>                 URL: https://issues.apache.org/jira/browse/HBASE-2180
>             Project: Hadoop HBase
>          Issue Type: Bug
>            Reporter: ryan rawson
>            Assignee: stack
>             Fix For: 0.20.4, 0.21.0
>
>         Attachments: 2180-v2.patch, 2180.patch
>
>
> deep in the HFile read path, there is this code:
>     synchronized (in) {
>       in.seek(pos);
>       ret = in.read(b, off, n);
>     }
> this makes it so that only 1 read per file per thread is active. this prevents the OS and hardware from being able to do IO scheduling by optimizing lots of concurrent reads. 
> We need to either use a reentrant API (pread may be partially reentrant according to Todd) or use multiple stream objects, 1 per scanner/thread.

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