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https://issues.apache.org/jira/browse/LUCENE-2793?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13048285#comment-13048285
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Michael McCandless commented on LUCENE-2793:
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bq. Can OneMerge extend MergeInfo?
I think this is risky because it then makes IOContext an unexpectedly
heavy object, since OneMerge holds SegmentReaders used for merging.
There are already some places that save away an IOContext instance as
a member (to be used later), and if something ever does this for a MERGE
then we can unexpectedly hold keep a lot of garbage alive.
I think, instead, when the context is MERGE, we should make a new
(lightweight) MergeInfo instance that pulls the necessary details from
the OneMerge, ie fully decouples from the OneMerge instance.
> 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: Varun Thacker
> Labels: gsoc2011, lucene-gsoc-11, mentor
> Attachments: LUCENE-2793.patch, LUCENE-2793.patch, LUCENE-2793.patch,
> LUCENE-2793.patch, LUCENE-2793.patch, LUCENE-2793.patch, LUCENE-2793.patch,
> 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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