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From "Michael McCandless (JIRA)" <>
Subject [jira] Commented: (LUCENE-2324) Per thread DocumentsWriters that write their own private segments
Date Thu, 22 Apr 2010 17:09:59 GMT


Michael McCandless commented on LUCENE-2324:

I'm not sure I understand how this would help for ParallelReader?
I think you can't use multi-threaded indexing even today, because you
have no control over the order in which the docs will make it into the

Well, to set up indexes for PR today, you have to run IndexWriter in a very degraded state
-- flush by doc count, use a single thread, turn off concurrent merging (use SMS), use LogDocMergePolicy.

So having maxBufferedDocs per DWPT seems tempting to me. Then you know
that each written segment will have exactly a size of maxBufferedDocs,
so this is much more predictable. And if you index with a single 
thread only the behavior is identical to a "global" maxBufferedDocs
flush trigger.
Yeah, maybe that'd be sufficient...?  It'd sort of "match" the current behaviour, in that
you get segments flushed to the index with that many docs.

> Per thread DocumentsWriters that write their own private segments
> -----------------------------------------------------------------
>                 Key: LUCENE-2324
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Michael Busch
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 3.1
>         Attachments: lucene-2324.patch, 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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