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From "Michael Busch (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-743) IndexReader.reopen()
Date Sat, 06 Oct 2007 06:56:50 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-743?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12532833
] 

Michael Busch commented on LUCENE-743:
--------------------------------------

> why use clones at all? why not just use the original reader (if the "index" that reader
represents hasn't changed, why clone it?

Let's say you have a MultiReader with two subreaders:
{code:java}
IndexReader ir1 = IndexReader.open(index1);
IndexReader ir2 = IndexReader.open(index2);
IndexReader mr = new MultiReader(new IndexReader[] {ir1, ir2});
{code}

Now index1 changes and you reopen the MultiReader and keep the old one open:

{code:java}
IndexReader mr2 = mr.reopen();
{code}

ir1 would now be reopened and let's assume we wouldn't clone ir2. If you use mr2 now to e.g.
delete a doc and that doc happens to be in index2, then mr1 would also see the changes because
both MultiReaders share the same subreader ir2 and are thus not independent from each other.

> why not make reopen always return this.clone()

clone() might be an expensive operation. We only need to clone if at least one of the subreaders
has changed.


> IndexReader.reopen()
> --------------------
>
>                 Key: LUCENE-743
>                 URL: https://issues.apache.org/jira/browse/LUCENE-743
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Otis Gospodnetic
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 2.3
>
>         Attachments: IndexReaderUtils.java, lucene-743-take2.patch, lucene-743.patch,
lucene-743.patch, lucene-743.patch, MyMultiReader.java, MySegmentReader.java
>
>
> This is Robert Engels' implementation of IndexReader.reopen() functionality, as a set
of 3 new classes (this was easier for him to implement, but should probably be folded into
the core, if this looks good).

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