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From "Eli Collins (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2982) Startup performance suffers when there are many edit log segments
Date Fri, 18 May 2012 05:22:10 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2982?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13278582#comment-13278582
] 

Eli Collins commented on HDFS-2982:
-----------------------------------

Hey Colin,

Took a quick look. How about describing the high-level approach in the patch?
- The javadoc for JournalSet#selectInputStreams is a little over-simplified =) - how about
describing the algorithm (get the streams starting with fromTxid from all managers, return
a list sorted by the starting txid etc) 
- In EditLogFileInputStream#init why only close the stream that threw?
- In TestEditLog readAllEdits is dead code


                
> Startup performance suffers when there are many edit log segments
> -----------------------------------------------------------------
>
>                 Key: HDFS-2982
>                 URL: https://issues.apache.org/jira/browse/HDFS-2982
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 2.0.0
>            Reporter: Todd Lipcon
>            Assignee: Colin Patrick McCabe
>            Priority: Critical
>         Attachments: HDFS-2982.001.patch
>
>
> For every one of the edit log segments, it seems like we are calling listFiles on the
edit log directory inside of {{findMaxTransaction}}. This is killing performance, especially
when there are many log segments and the directory is stored on NFS. It is taking several
minutes to start up the NN when there are several thousand log segments present.

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