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From "Yonik Seeley (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2825) FSDirectory.open should return MMap on 64-bit Solaris
Date Mon, 20 Dec 2010 17:14:16 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12973260#action_12973260
] 

Yonik Seeley commented on LUCENE-2825:
--------------------------------------

There could be a number of things that could make this very OS dependent:
 - kernel read-ahead can differ between mmap and traditional IO, and differ between operating
systems
   (think about reading 10 bytes from position 4094... if mmap doesn't read-ahead at least
one page then you will suffer a double page fault).
 - CPU cache / TLB effects?  Using more address space isn't completely free.
 - Java mmap overhead - you don't get access to a raw byte[]
 - userspace-kernel transition times (i.e. for a read system call) differ between operating
systems.  Linux is very good here, probably leading to less of a penalty for read vs mmap.


> FSDirectory.open should return MMap on 64-bit Solaris
> -----------------------------------------------------
>
>                 Key: LUCENE-2825
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2825
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Store
>            Reporter: Robert Muir
>             Fix For: 3.1, 4.0
>
>         Attachments: LUCENE-2825.patch
>
>
> MMap is ~ 30% faster than NIOFS on this platform.

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