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Date: Sun, 3 Jun 2012 10:17:23 +0000 (UTC)
From: "Uwe Schindler (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
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Subject: [jira] [Commented] (LUCENE-2858) Separate SegmentReaders (and other
 atomic readers) from composite IndexReaders
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    [ https://issues.apache.org/jira/browse/LUCENE-2858?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13288133#comment-13288133 ] 

Uwe Schindler commented on LUCENE-2858:
---------------------------------------

Thanks Mike for taking care. For me this looked crazy, because refactoring like this should not change perf.

This explains the change back  after 4055, I thought un-compressed oops responsible for the speedup.
                
> Separate SegmentReaders (and other atomic readers) from composite IndexReaders
> ------------------------------------------------------------------------------
>
>                 Key: LUCENE-2858
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2858
>             Project: Lucene - Java
>          Issue Type: Task
>            Reporter: Uwe Schindler
>            Assignee: Uwe Schindler
>            Priority: Blocker
>             Fix For: 4.0
>
>         Attachments: LUCENE-2858-FCinsanity.patch, LUCENE-2858-FixSlowEnsureOpen.patch, LUCENE-2858.patch, LUCENE-2858.patch
>
>
> With current trunk, whenever you open an IndexReader on a directory you get back a DirectoryReader which is a composite reader. The interface of IndexReader has now lots of methods that simply throw UOE (in fact more than 50% of all methods that are commonly used ones are unuseable now). This confuses users and makes the API hard to understand.
> This issue should split "atomic readers" from "reader collections" with a separate API. After that, you are no longer able, to get TermsEnum without wrapping from those composite readers. We currently have helper classes for wrapping (SlowMultiReaderWrapper - please rename, the name is really ugly; or Multi*), those should be retrofitted to implement the correct classes (SlowMultiReaderWrapper would be an atomic reader but takes a composite reader as ctor param, maybe it could also simply take a List<AtomicReader>). In my opinion, maybe composite readers could implement some collection APIs and also have the ReaderUtil method directly built in (possibly as a "view" in the util.Collection sense). In general composite readers do not really need to look like the previous IndexReaders, they could simply be a "collection" of SegmentReaders with some functionality like reopen.
> On the other side, atomic readers do not need reopen logic anymore? When a segment changes, you need a new atomic reader? - maybe because of deletions thats not the best idea, but we should investigate. Maybe make the whole reopen logic simplier to use (ast least on the collection reader level).
> We should decide about good names, i have no preference at the moment.

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