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https://issues.apache.org/jira/browse/LUCENE-3092?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13033240#comment-13033240
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Michael McCandless commented on LUCENE-3092:
--------------------------------------------
{quote}
IOCtx should have a value 'expectedSize', or 'priority', or something similar.
This does not introduce a transitive dependency of Directory from MergePolicy
(to please you once more - a true WTF),
{quote}
Ahh, good point. So, for this dir impl I want to say "if net seg size is < X
MB, cache it in RAM", so I guess we could have something like
"expectedSizeOfSegmentMB" (covers all files that will be flushed for this
segment, hmm minus the doc stores) in the IOCtx.
> NRTCachingDirectory, to buffer small segments in a RAMDir
> ---------------------------------------------------------
>
> Key: LUCENE-3092
> URL: https://issues.apache.org/jira/browse/LUCENE-3092
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Store
> Reporter: Michael McCandless
> Priority: Minor
> Fix For: 3.2, 4.0
>
> Attachments: LUCENE-3092-listener.patch, LUCENE-3092.patch
>
>
> I created this simply Directory impl, whose goal is reduce IO
> contention in a frequent reopen NRT use case.
> The idea is, when reopening quickly, but not indexing that much
> content, you wind up with many small files created with time, that can
> possibly stress the IO system eg if merges, searching are also
> fighting for IO.
> So, NRTCachingDirectory puts these newly created files into a RAMDir,
> and only when they are merged into a too-large segment, does it then
> write-through to the real (delegate) directory.
> This lets you spend some RAM to reduce I0.
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