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