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From "Earwin Burrfoot (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1743) MMapDirectory should only mmap large files, small files should be opened using SimpleFS/NIOFS
Date Wed, 15 Jul 2009 19:28:14 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1743?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12731639#action_12731639
] 

Earwin Burrfoot commented on LUCENE-1743:
-----------------------------------------

bq. My problem was more with all these small files like segments_XXXX and segments.gen or
*.del files. They are small and only used one time.
I can only reiterate my point. These files aren't opened like 10k files per second, so your
win is going to be in the order of microseconds per reopen - at the cost of increased complexity.

> 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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