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Date: Fri, 3 Dec 2010 07:43:10 -0500 (EST)
From: "Robert Muir (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-2791) WindowsDirectory
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    [ https://issues.apache.org/jira/browse/LUCENE-2791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12966512#action_12966512 ] 

Robert Muir commented on LUCENE-2791:
-------------------------------------

bq. Does is also allow for deletion of still-open files?

No, but we could/should investigate trying to improve this, thoguh we might have to implement IndexOutput for it to all work.

bq. You may want to experiment w/ different buffer sizes to see if that impacts performance.

maybe, mainly my point was to avoid the synchronized() here. A user could always tweak the buffer size here?

bq. Also: this allows you to do the equivalent of Linux's O_DIRECT, right? If so... I think we should augment the Dir API so that on opening an input it receives some sort of IOContext or something expressing why we are opening. So for merging we would want "direct iO" (bypass OS buffer cache or NOREUSE fadvise flag, etc.), and larger buffer sizes and perhaps other low level IO settings in the future.

Yes, we can use FILE_FLAG_NO_BUFFERING, though it would be more complicated (things must be sector-aligned). In my opinion this should be a separate IndexInput, and as you stated the Dir API  could inform us. But you are right, the general notion seems to be in all major platforms, and I think we should carefully use it (if it can help!)


> WindowsDirectory
> ----------------
>
>                 Key: LUCENE-2791
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2791
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: Store
>            Reporter: Robert Muir
>         Attachments: LUCENE-2791.patch, LUCENE-2791.patch, WindowsDirectory.dll, WindowsDirectory_amd64.dll
>
>
> We can use Windows' overlapped IO to do pread() and avoid the performance problems of SimpleFS/NIOFSDir.

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