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From "Yonik Seeley (JIRA)" <>
Subject [jira] Commented: (LUCENE-2324) Per thread DocumentsWriters that write their own private segments
Date Thu, 22 Jul 2010 16:56:55 GMT


Yonik Seeley commented on LUCENE-2324:

bq. It'd also be nice to have a more efficient data structure to buffer the deletes. With
many buffered deletes the java hashmap approach will not be very efficient. Terms could be
written into a byte pool, but what should we do with queries?

IMO, terms are an order of magnitude more important than queries.  Most deletes will be by
some sort of unique id, and will be in the same field.

Perhaps a single byte[] with length prefixes (like the field cache has).  A single int could
then represent a term (it would just be an offset into the byte[], which is field-specific,
so no need to store the field each time).

We could then build a treemap or hashmap that natively used an int[]... but that may not be
necessary (depending on how deletes are applied).  Perhaps a sort could be done right before
applying, and duplicate terms could be handled at that time.

Anyway, I'm only casually following this issue, but I'ts looking like really cool stuff!

> 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.patch, 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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