hadoop-hdfs-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Todd Lipcon (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-2533) Remove needless synchronization on FSDataSet.getBlockFile
Date Wed, 02 Nov 2011 20:49:32 GMT

     [ https://issues.apache.org/jira/browse/HDFS-2533?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon updated HDFS-2533:
------------------------------

    Attachment: hdfs-2533.txt

Here's the simple patch.

The reason this is correct is follows:

- getBlockFile() doesn't itself access any in-memory structures. It calls validateBlockFile
- validateBlockFile is unsynchronized. It also doesn't access any structures. It calls getFile()
which _is_ synchronized (since it accesses in-memory state). Then it calls f.exists().
- it's safe to call f.exists() outside the lock because, even if we had the lock, someone
could remove the file just after we exit this function.
                
> Remove needless synchronization on FSDataSet.getBlockFile
> ---------------------------------------------------------
>
>                 Key: HDFS-2533
>                 URL: https://issues.apache.org/jira/browse/HDFS-2533
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: data-node
>    Affects Versions: 0.23.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Minor
>         Attachments: hdfs-2533.txt
>
>
> HDFS-1148 discusses lock contention issues in FSDataset. It provides a more comprehensive
fix, converting it all to RWLocks, etc. This JIRA is for one very specific fix which gives
a decent performance improvement for TestParallelRead: getBlockFile() currently holds the
lock which is completely unnecessary.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira

        

Mime
View raw message