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From "Michael Busch (JIRA)" <>
Subject [jira] Commented: (LUCENE-2324) Per thread DocumentsWriters that write their own private segments
Date Mon, 29 Mar 2010 20:36:35 GMT


Michael Busch commented on LUCENE-2324:

I'm not sure we need that level of complexity just yet? How
would we make the transaction log memory efficient?

Is that really so complex?  You only need one additional int per doc in the DWPTs, and the
global map for the delete terms.  You don't need to buffer the actual terms per DWPT.  I thought
that's quite efficient?  But I'm totally open to other ideas.

I can try tonight to code a prototype of this - I don't think it would be very complex actually.
 But of course there might be complications I haven't thought of.

bq.  Are there other uses you foresee?

Not really for the "transaction log" as you called it.  I'd remove that log once we switch
to deletes in the FG (when the RAM buffer is searchable).  But a nice thing would be for add/update/delete
to return the seqID, and also the if RAMReader in the future had an API to check up to which
seqID it's able to "see".  Then it's very clear to user of the API where a given reader is
For this to work we have to assign the seqID at the *end* of a call.  E.g. when adding a large
document, which takes a long time to process, it should get the seqID assigned after the "work"
is done and right before the addDocument() call returns.  

> 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
> 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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