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Date: Thu, 19 Feb 2009 17:20:01 -0800 (PST)
From: "Jason Rutherglen (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-1516) Integrate IndexReader with
 IndexWriter
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    [ https://issues.apache.org/jira/browse/LUCENE-1516?page=3Dcom.atlassia=
n.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D126=
75206#action_12675206 ]=20

Jason Rutherglen commented on LUCENE-1516:
------------------------------------------

The path forward seems to be exposing a cloned readonly reader
from IW.getReader. This would be easier than doing hula hoops to do
segment genealogy (at least for now =E2=98=BA)

{quote}can't we move away from allowing any changes via IR? (Ie
deprecate deleteDocuments/setNorms/etc.){quote}

This would simplify things however as a thought experiment how would
the setNorms work if it were a part of IndexWriter?=20

{quote} And, clone should not be reopening segments...? {quote}

DirectoryIndexReader.clone(boolean openReadonly) calls
doReopen(SegmentInfos infos, boolean doClone, boolean openReadOnly)
which is an abstract method that in SegmentReader and
MultiSegmentReader reopens the segments? The segment infos for a
ReaderIW is obtained from IW, which is how it knows about the new
segments. Perhaps not desired behavior?

{quote} do we need delete by docID once we have realtime search? I
think the last compelling reason to keep IR's delete by docID was
immediacy, but realtime search can give us that, from IW, even when
deleting by Term or Query? {quote}

Good point! I think we may want to support it but for now it's
shouldn't be necessary. I'm thinking of the case where someone is
using the field cache (or some variant), performs some sort of query
on it and then needs to delete based on doc id. What do they do?
Would we expose a callback mechanism where a deleteFrom(IndexReader
ir) method is exposed and deletes occur at the time of the IW's
choosing?

{quote} It seems like calling reader.reopen() (on reader obtained
from writer) should basically do the same thing as calling
writer.getReader(). Ie they are nearly synonyms? (Except for small
difference in ref counting - I think writer.getReader() should always
incRef, but reopen only incRefs if it returns a new reader). {quote}

Perhaps ReaderIW.reopen will call IW.getReader underneath instead of
using IR's usual mechanism.


> Integrate IndexReader with IndexWriter=20
> ---------------------------------------
>
>                 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
>            Priority: Minor
>             Fix For: 2.9
>
>         Attachments: LUCENE-1516.patch, LUCENE-1516.patch, LUCENE-1516.pa=
tch, 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.=20
> 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.=20

--=20
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