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https://issues.apache.org/jira/browse/LUCENE-1313?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12702515#action_12702515
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Michael McCandless commented on LUCENE-1313:
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bq. I don't think it's necessary to immediately write ram segments to disk
I agree: it should be fine from IndexWriter's standpoint if some
segments live in a private RAMDir and others live in the "real" dir.
In fact, early versions of LUCENE-843 did exactly this: IW's RAM
buffer is not as efficient as a written segment, and so you can gain
some RAM efficiency by flushing first to RAM and then merging to disk.
I think we could adopt a simple criteria: you flush the new segment to
the RAM Dir if net RAM used is < maxRamBufferSizeMB. This way no
further configuration is needed. On auto-flush triggering you then
must take into account the RAM usage by this RAM Dir. On commit,
these RAM segments must be migrated to the real dir (preferably by
forcing a merge, somehow).
A near realtime reader would also happily mix "real" Dir and RAMDir
SegmentReaders.
This should work well I think, and should not require a separate
RAMIndex class, and won't block things when the RAM segments are
migrated to disk by CMS.
> Realtime Search
> ---------------
>
> Key: LUCENE-1313
> URL: https://issues.apache.org/jira/browse/LUCENE-1313
> Project: Lucene - Java
> Issue Type: New Feature
> Components: Index
> Affects Versions: 2.4.1
> Reporter: Jason Rutherglen
> Priority: Minor
> Fix For: 2.9
>
> Attachments: LUCENE-1313.jar, LUCENE-1313.patch, LUCENE-1313.patch,
> LUCENE-1313.patch, LUCENE-1313.patch, lucene-1313.patch, lucene-1313.patch,
> lucene-1313.patch, lucene-1313.patch
>
>
> Realtime search with transactional semantics.
> Possible future directions:
> * Optimistic concurrency
> * Replication
> Encoding each transaction into a set of bytes by writing to a RAMDirectory
> enables replication. It is difficult to replicate using other methods
> because while the document may easily be serialized, the analyzer cannot.
> I think this issue can hold realtime benchmarks which include indexing and
> searching concurrently.
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