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From "Uwe Schindler (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4364) MMapDirectory makes too many maps for CFS
Date Thu, 06 Sep 2012 12:05:08 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4364?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13449591#comment-13449591
] 

Uwe Schindler commented on LUCENE-4364:
---------------------------------------

I forgot to mention: My patch also fixes a "small bug" in MMapIndexInput: If you closed a
clone, this did not change it's state at all, the close() method of clones was completely
ignored. I changed that to at least unset the buffers for this clone/slice, so later calls
throw AlreadyClosed. Clones of that one (previously created) are not affected. The top-level
cleanup also unsets all clones of course again, but thats fine. Theoretically, "closed" clones
could be removed from the map, but that is unneeded, because they will diappear automatically
(as soon as they are unreferenced).
                
> MMapDirectory makes too many maps for CFS
> -----------------------------------------
>
>                 Key: LUCENE-4364
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4364
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Robert Muir
>         Attachments: LUCENE-4364.patch, LUCENE-4364.patch, LUCENE-4364.patch, LUCENE-4364.patch,
LUCENE-4364.patch
>
>
> While looking at LUCENE-4123, i thought about this:
> I don't like how mmap creates a separate mapping for each CFS slice, to me this is way
too many mmapings.
> Instead I think its slicer should map the .CFS file, and then when asked for an offset+length
slice of that, it should be using .duplicate()d buffers of that single master mapping.
> then when you close the .CFS it closes that one mapping.
> this is probably too scary for 4.0, we should take our time, but I think we should do
it.

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