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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1743) MMapDirectory should only mmap large files, small files should be opened using SimpleFS/NIOFS
Date Tue, 14 Jul 2009 20:05:14 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1743?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12731091#action_12731091
] 

Michael McCandless commented on LUCENE-1743:
--------------------------------------------

At a minimum we should make FileSwitchDirectory friendly for subclassing, eg so you can override
the currently private getDirectory method to implement your own custom logic.  Hmm... we should
somehow pass the "context" (at least 'read' vs 'write') to getDirectory() as well...

> MMapDirectory should only mmap large files, small files should be opened using SimpleFS/NIOFS
> ---------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-1743
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1743
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Store
>    Affects Versions: 2.9
>            Reporter: Uwe Schindler
>            Assignee: Uwe Schindler
>             Fix For: 3.1
>
>
> This is a followup to LUCENE-1741:
> Javadocs state (in FileChannel#map): "For most operating systems, mapping a file into
memory is more expensive than reading or writing a few tens of kilobytes of data via the usual
read and write methods. From the standpoint of performance it is generally only worth mapping
relatively large files into memory."
> MMapDirectory should get a user-configureable size parameter that is a lower limit for
mmapping files. All files with a size<limit should be opened using a conventional IndexInput
from SimpleFS or NIO (another configuration option for the fallback?).

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