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From "Michael Busch (JIRA)" <>
Subject [jira] Commented: (LUCENE-2324) Per thread DocumentsWriters that write their own private segments
Date Wed, 19 Jan 2011 08:38:48 GMT


Michael Busch commented on LUCENE-2324:

So I'm wondering about the following problem with deletes:

Suppose we open a new IW on an existing index with 2 segments _1 and _2. IW is set to maxBufferedDocs=1000.
 The app starts indexing with two threads, so two DWPTs are created.  DWPT1 starts working
on _3, DWPT2 on _4.  Both "remember" that they must apply their deletes only to segments _1
and _2.  After adding 500 docs thread 2 stops indexing for an hour, but thread 1 keeps working.
 While thread 2 is sleeping several segment flushes (_3, _5, _6, etc) happen.

Now thread 2 wakes up again and adds another 500 docs, and also some deletes, so DWPT2 has
to flush finally.  How can it figure out to which docs the deletes to apply to?  _1 and _2
are probably gone a long time ago.  If we apply the deletes to all of _3 this would be a mistake

I'm starting to think there's no way around sequenceIds?  Even without RT.

> 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: Realtime Branch
>         Attachments: LUCENE-2324-SMALL.patch, LUCENE-2324-SMALL.patch, LUCENE-2324-SMALL.patch,
LUCENE-2324-SMALL.patch, LUCENE-2324-SMALL.patch, LUCENE-2324.patch, LUCENE-2324.patch, LUCENE-2324.patch,
lucene-2324.patch, lucene-2324.patch, LUCENE-2324.patch, test.out, test.out, test.out, test.out
> 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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