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https://issues.apache.org/jira/browse/LUCENE-2858?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13287563#comment-13287563
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Michael McCandless commented on LUCENE-2858:
--------------------------------------------
Not entirely sure why but it looks like the commits here slowed down our NRT
reopen latency. If you look at the nightly bench graph:
http://people.apache.org/~mikemccand/lucenebench/nrt.html and click + drag from
Jan 2012 to today, annotation R shows we increased from ~46 msec NRT reopen
latency to ~50 msec ... could just be hotspot being upset...
> 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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