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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1526) For near real-time search, use paged copy-on-write BitVector impl
Date Tue, 10 Nov 2009 10:48:27 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1526?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12775373#action_12775373
] 

Michael McCandless commented on LUCENE-1526:
--------------------------------------------

{quote}
bq. One optimization you could make with Zoie is, if a real-time deletion (from the AcceleratedIntSet)
is in fact hit, it could mark the corresponding docID, to make subsequent searches a bit faster
(and save the bg CPU when flushing the deletes to Lucene).

That sound interesting - how would that work? We don't really touch the disk indexReader,
other than to set this modSet on it in the ThreadLocal, where would this mark live?
{quote}

Whenever a query happens to "discover" a pending deletion, you could
record somewhat the UID -> docID mapping, and then when it's time to
flush the deletes you don't need to re-resolve the UIDs that the query
had resolved for you.  Likely in practice this would be a tiny
speedup, though, so the added complexity is probably not worth it.
Especially since this resolution is done in the BG for Zoie...


> For near real-time search, use paged copy-on-write BitVector impl
> -----------------------------------------------------------------
>
>                 Key: LUCENE-1526
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1526
>             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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