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Date: Wed, 2 Nov 2011 22:47:32 +0000 (UTC)
From: "Todd Lipcon (Updated) (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Updated] (HDFS-2533) Remove needless synchronization on
 FSDataSet.getBlockFile
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     [ 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

Slightly improved version. I found it was pretty trivial to fix contention in two other places: in these places we were doing a lock around an file.exists() call unnecessarily, since we were about to open the file for read right afterwards. Given that, the exists check is unnecessary - we'll get FileNotFoundException when we try to read the file.

With this patch the numbers improve to:

| Threads | Trunk  | HDFS-2533v2           |
| 4 | 226556 KB/s  | 237805 KB/sec (1.05x) |
| 16 | 377474 KB/s | 499399 KB/sec (1.32x) |
| 8 | 410114 KB/s  | 474560 KB/sec (1.15x) |

                
> 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-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.

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