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From "Jason Rutherglen (JIRA)" <>
Subject [jira] Commented: (LUCENE-1526) For near real-time search, use paged copy-on-write BitVector impl
Date Mon, 09 Nov 2009 19:05:32 GMT


Jason Rutherglen commented on LUCENE-1526:

{quote} check out the zoie perf pages:
ieLucene24ZoieLucene29LuceneNRT {quote}

What's missing as it pertains to this jira issue is the raw
query speed (meaning the time a query takes to execute, not QPS,
over various percentages of deleted docs), without concurrent

If query speed goes down, users need to know by how much. 

> For near real-time search, use paged copy-on-write BitVector impl
> -----------------------------------------------------------------
>                 Key: LUCENE-1526
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>    Affects Versions: 2.4
>            Reporter: Jason Rutherglen
>            Priority: Minor
>         Attachments: LUCENE-1526.patch
>   Original Estimate: 168h
>  Remaining Estimate: 168h
> SegmentReader currently uses a BitVector to represent deleted docs.
> When performing rapid clone (see LUCENE-1314) and delete operations,
> performing a copy on write of the BitVector can become costly because
> the entire underlying byte array must be created and copied. A way to
> make this clone delete process faster is to implement tombstones, a
> term coined by Marvin Humphrey. Tombstones represent new deletions
> plus the incremental deletions from previously reopened readers in
> the current reader. 
> The proposed implementation of tombstones is to accumulate deletions
> into an int array represented as a DocIdSet. With LUCENE-1476,
> SegmentTermDocs iterates over deleted docs using a DocIdSet rather
> than accessing the BitVector by calling get. This allows a BitVector
> and a set of tombstones to by ANDed together as the current reader's
> delete docs. 
> A tombstone merge policy needs to be defined to determine when to
> merge tombstone DocIdSets into a new deleted docs BitVector as too
> many tombstones would eventually be detrimental to performance. A
> probable implementation will merge tombstones based on the number of
> tombstones and the total number of documents in the tombstones. The
> merge policy may be set in the clone/reopen methods or on the
> IndexReader. 

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