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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-2795) Genericize DirectIOLinuxDir -> UnixDir
Date Sun, 24 Apr 2011 15:28:06 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2795?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13024631#comment-13024631
] 

Michael McCandless commented on LUCENE-2795:
--------------------------------------------

Today, we don't use any of these flags for searching/merging (that's what this issue and LUCENE-2793
will fix).

Unfortunately, it looks like the best IO flags are going to vary depending on kernel version.
 The above patch was applied in kernel 2.6.29, and causes SEQUENTIAL to act like NOREUSE,
and so we should use SEQUENTIAL for merging but not for searching, I think?  We should experiment
and see...

Really, for searching we want the "old" SEQUENTIAL behavior (ie, do aggressive readahead,
but use the normal eviction policy since that term may be searched on again).

Hopefully NativeUnixDir will take care of all these os/kernel-version dependent flags for
you.

> Genericize DirectIOLinuxDir -> UnixDir
> --------------------------------------
>
>                 Key: LUCENE-2795
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2795
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Store
>            Reporter: Michael McCandless
>            Assignee: Simon Willnauer
>              Labels: gsoc2011, lucene-gsoc-11, mentor
>
> Today DirectIOLinuxDir is tricky/dangerous to use, because you only want to use it for
indexWriter and not IndexReader (searching).  It's a trap.
> But, once we do LUCENE-2793, we can make it fully general purpose because then a single
native Dir impl can be used.
> I'd also like to make it generic to other Unices, if we can, so that it becomes UnixDirectory.

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