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Date: Sat, 27 Mar 2010 09:46:27 +0000 (UTC)
From: "Michael McCandless (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-2324) Per thread DocumentsWriters that
 write their own private segments
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    [ https://issues.apache.org/jira/browse/LUCENE-2324?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12850500#action_12850500 ] 

Michael McCandless commented on LUCENE-2324:
--------------------------------------------

I don't think we should delete in FG -- I suspect this'll give net/net worse performance, due to loss of locality.  It also means you must always keep readers available, which is an unnecessary cost for non-NRT apps.

deletesInRAM are those deletes done during the current segment.  deletesFlushed absorbs deletesInRAM on successful segment flush.  We have to segregate the two for proper recovery if we fail to flush the RAM buffer, eg say you hit a disk full while flushing a new segment, and then you close your IW successfully.  We have to make sure in that case that deletesInRAM are discarded.

> Per thread DocumentsWriters that write their own private segments
> -----------------------------------------------------------------
>
>                 Key: LUCENE-2324
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2324
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Michael Busch
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 3.1
>
>         Attachments: LUCENE-2324.patch
>
>
> See LUCENE-2293 for motivation and more details.
> I'm copying here Mike's summary he posted on 2293:
> Change the approach for how we buffer in RAM to a more isolated
> approach, whereby IW has N fully independent RAM segments
> in-process and when a doc needs to be indexed it's added to one of
> them. Each segment would also write its own doc stores and
> "normal" segment merging (not the inefficient merge we now do on
> flush) would merge them. This should be a good simplification in
> the chain (eg maybe we can remove the *PerThread classes). The
> segments can flush independently, letting us make much better
> concurrent use of IO & CPU.

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