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Date: Mon, 30 May 2011 18:33:47 +0000 (UTC)
From: "Michael McCandless (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
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Subject: [jira] [Commented] (LUCENE-2793) Directory createOutput and
 openInput should take an IOContext
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    [ https://issues.apache.org/jira/browse/LUCENE-2793?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13041225#comment-13041225 ] 

Michael McCandless commented on LUCENE-2793:
--------------------------------------------

bq. Some kind of a copy-on-write builder pattern

Why not use a normal struct/bean like class here?

bq. I wonder if it makes sense to bind the IO Context instance to the directory and add a factory to the directory like Directory#getIOContext(Merge|Search|Index) to enable the directory impl to set platform specific defaults

Hmm, but, if the IOCtxt is 'high level', and then details (bufferSize, seq/direct flags, etc.) are private to the dir impl, I think we (Lucene) can create the IOCtx and pass it down?  Ie this is a one-way communication, I think (Lucene -> Dir impl).

> Directory createOutput and openInput should take an IOContext
> -------------------------------------------------------------
>
>                 Key: LUCENE-2793
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2793
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: core/store
>            Reporter: Michael McCandless
>            Assignee: Simon Willnauer
>              Labels: gsoc2011, lucene-gsoc-11, mentor
>         Attachments: LUCENE-2793.patch, LUCENE-2793.patch, LUCENE-2793.patch
>
>
> Today for merging we pass down a larger readBufferSize than for searching because we get better performance.
> I think we should generalize this to a class (IOContext), which would hold the buffer size, but then could hold other flags like DIRECT (bypass OS's buffer cache), SEQUENTIAL, etc.
> Then, we can make the DirectIOLinuxDirectory fully usable because we would only use DIRECT/SEQUENTIAL during merging.
> This will require fixing how IW pools readers, so that a reader opened for merging is not then used for searching, and vice/versa.  Really, it's only all the open file handles that need to be different -- we could in theory share del docs, norms, etc, if that were somehow possible.

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