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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1516) Integrate IndexReader with IndexWriter
Date Fri, 06 Mar 2009 23:03:56 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1516?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12679758#action_12679758
] 

Michael McCandless commented on LUCENE-1516:
--------------------------------------------


bq. Where should I get the numDeletedDocs from?

SegmentMerger.getDelCounts()

bq. Should the entire docIdMap be scanned?

Yes, when the before/after delCount is different.

bq. Is there an expense in cloning the segment readers besides the extra bitvectors?

Copy-on-write of the bitvectors (time and space) is the biggest cost I
think.  Since docMap already has everything we need, I think we should
use it... we could even separate out this change and do it first, if
you want.

{quote}
I think you're saying put this patch's decRef logic in
the SRP.release method?
{quote}

Actually the release method should always commit changes, if there are
any, when an SR is removed SR from the pool.

Then, something higher up (merging, once successful) should clear
changes when it's safe, so that release doesn't save anything.

The "decRef that never commits whenever writer is present" in
DirectoryIndexReader is too low level, I think.


> Integrate IndexReader with IndexWriter 
> ---------------------------------------
>
>                 Key: LUCENE-1516
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1516
>             Project: Lucene - Java
>          Issue Type: Improvement
>    Affects Versions: 2.4
>            Reporter: Jason Rutherglen
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.9
>
>         Attachments: LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch,
LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch,
LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch,
LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch,
LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.patch
>
>   Original Estimate: 672h
>  Remaining Estimate: 672h
>
> The current problem is an IndexReader and IndexWriter cannot be open
> at the same time and perform updates as they both require a write
> lock to the index. While methods such as IW.deleteDocuments enables
> deleting from IW, methods such as IR.deleteDocument(int doc) and
> norms updating are not available from IW. This limits the
> capabilities of performing updates to the index dynamically or in
> realtime without closing the IW and opening an IR, deleting or
> updating norms, flushing, then opening the IW again, a process which
> can be detrimental to realtime updates. 
> This patch will expose an IndexWriter.getReader method that returns
> the currently flushed state of the index as a class that implements
> IndexReader. The new IR implementation will differ from existing IR
> implementations such as MultiSegmentReader in that flushing will
> synchronize updates with IW in part by sharing the write lock. All
> methods of IR will be usable including reopen and clone. 

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