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