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From John Wang <john.w...@gmail.com>
Subject Re: 2.9 NRT w.r.t. sorting and field cache
Date Wed, 23 Sep 2009 00:26:56 GMT
Mark:

I did spend at least a quarter of an ounce. :) And I am sure Mike's time is
more valuable than mine, but it was meant to be a "double-check"

I was under the impression there is a default impl from previous email
threads on how to handle field cache warming, perhaps I misunderstood.

The real question here is "warms the reader" From a public API point of
view, I wasn't sure if passing in a IndexReader impl is something we can do
to avoid loading the entire field cache. e.g. would I need to down cast? can
it be a filtered reader? etc.

If you think there is something I could have done witin 5 sec, please point
me to the right direction.

Thanks

-John

On Wed, Sep 23, 2009 at 7:55 AM, Mark Miller <markrmiller@gmail.com> wrote:

> Come on dude :) Spend a half ounce of effort first. Mike's time is too
> valuable !
>
> Luckily mine is not.
>
> There is no default impl - the class is dead simple (and the class has
> been pointed out like 3 times in this thread - I'm not even fully
> following and I know where to find it):
>
>  public static abstract class IndexReaderWarmer {
>    public abstract void warm(IndexReader reader) throws IOException;
>  }
>
> Now pass something in that warms the reader. Load a fieldcache - do a
> search. Do the hokey pokey and turn your self around ...
>
> Investigation time: 5 seconds.
>
> John Wang wrote:
> > Hi Michael:
> >
> >      Thanks for the pointer!
> >
> >       Pardon my ignorance, but I am still no seeing the connection
> > between this api to per/segment loading of FieldCache. (the api takes
> > in an IndexReader instead of maybe SegmentReader[])
> >
> >       Can you point me to maybe the default impl of IndexReaderWarmer
> > to help me understand?
> >
> > Thanks
> >
> > -John
> >
> > On Wed, Sep 23, 2009 at 7:17 AM, Michael McCandless
> > <lucene@mikemccandless.com <mailto:lucene@mikemccandless.com>> wrote:
> >
> >     This is exactly why we added IndexWriter.setMergedSegmentWarmer --
> you
> >     can warm the reader w/o blocking ongoing updates.
> >
> >     Mike
> >
> >     On Tue, Sep 22, 2009 at 7:15 PM, Mark Miller
> >     <markrmiller@gmail.com <mailto:markrmiller@gmail.com>> wrote:
> >     > Right - when a large segment is invalidated, you will have a bigger
> >     > fieldcache piece to reload - pre 2.9, you'd be reloading the
> *whole*
> >     > field cache every time though. Sounds like you are trying to
> >     deal with
> >     > those large segments changing anyway :) They are always an issue
> >     when
> >     > doing RT it seems.
> >     >
> >     > I don't believe deletes invalidate a field cache - terms from
> >     deleted
> >     > docs stay in a field cache and segmentreaders use their
> >     freqStream as
> >     > the fieldcache key. Only when the deletes are merged out would they
> >     > invalidate - but because your writing a new segment anyway ...
> >     >
> >     > - Mark
> >     >
> >     > John Wang wrote:
> >     >> I understand what you are saying. Let me detail what I am
> >     trying to say:
> >     >>
> >     >> When "currently processed segments" are flushed down, merge may
> >     >> happen. When merges happen, some of those "stable segments" will
> be
> >     >> invalidated, and so will the fieldcache data keyed by them.
> >     >>
> >     >> In a high update environment, such scenarios can happen quite
> >     often.
> >     >>
> >     >> The way the default mergePolicy works is that small segments get
> >     >> merged into the larger segments. Eventually, what will be
> >     invalidated
> >     >> would be a large segment, and when that happens, a large chunk
> >     of the
> >     >> field cache would be invalidated.
> >     >>
> >     >> Furthermore, in the case where there are high updates, the stable
> >     >> segments can be invalidate much sooner when there are deletes
> >     in those
> >     >> segments, and I would guess the corresponding FieldCache needs
> >     to be
> >     >> adjusted. Not sure how it is handled right now.
> >     >>
> >     >> Just my two cents, and of course when I find the time I will
> >     need to
> >     >> run some tests to see.
> >     >>
> >     >> -John
> >     >>
> >     >> On Tue, Sep 22, 2009 at 3:59 PM, Uwe Schindler <uwe@thetaphi.de
> >     <mailto:uwe@thetaphi.de>
> >     >> <mailto:uwe@thetaphi.de <mailto:uwe@thetaphi.de>>> wrote:
> >     >>
> >     >>     The NRT reader coming from the IndexWriter.getReader() has
> only
> >     >>     changes in the currently processed segments, the other
> segments
> >     >>     keep stable (and even their IndexReader keys used for the
> >     >>     FieldCache). The rest of the segments keep stable. For the
> >     >>     consumer it looks like a normal reader (it is in fact a
> >     >>     ReadOnlyDirectoryReader) supporting
> >     getSequentialSubReaders() and
> >     >>     so on.
> >     >>
> >     >>
> >     >>
> >     >>     -----
> >     >>     Uwe Schindler
> >     >>     H.-H.-Meier-Allee 63, D-28213 Bremen
> >     >>     http://www.thetaphi.de
> >     >>     eMail: uwe@thetaphi.de <mailto:uwe@thetaphi.de>
> >     <mailto:uwe@thetaphi.de <mailto:uwe@thetaphi.de>>
> >     >>
> >     >>
> >
> ------------------------------------------------------------------------
> >     >>
> >     >>     *From:* John Wang [mailto:john.wang@gmail.com
> >     <mailto:john.wang@gmail.com>
> >     >>     <mailto:john.wang@gmail.com <mailto:john.wang@gmail.com>>]
> >     >>     *Sent:* Tuesday, September 22, 2009 9:32 AM
> >     >>     *To:* java-dev@lucene.apache.org
> >     <mailto:java-dev@lucene.apache.org>
> >     <mailto:java-dev@lucene.apache.org
> >     <mailto:java-dev@lucene.apache.org>>
> >     >>     *Subject:* Re: 2.9 NRT w.r.t. sorting and field cache
> >     >>
> >     >>
> >     >>
> >     >>     Thanks Mark for the pointer!
> >     >>
> >     >>     I guess my point is with NRT, and when segment files change
> >     often,
> >     >>     this would be an issue, no?
> >     >>
> >     >>     Anyway, I can run some tests.
> >     >>
> >     >>     Thanks
> >     >>
> >     >>     -John
> >     >>
> >     >>     On Tue, Sep 22, 2009 at 3:21 PM, Mark Miller
> >     >>     <markrmiller@gmail.com <mailto:markrmiller@gmail.com>
> >     <mailto:markrmiller@gmail.com <mailto:markrmiller@gmail.com>>>
> wrote:
> >     >>
> >     >>     1483 - indexsearcher pulls out a readers subreaders
> >     >>     (segmentreaders) and sends a collector over them one by one,
> >     >>     rather than using the multireader. So only fc for seg
> >     readers that
> >     >>     change need to be reloaded.
> >     >>
> >     >>     - Mark
> >     >>
> >     >>
> >     >>
> >     >>     http://www.lucidimagination.com (mobile)
> >     >>
> >     >>
> >     >>     On Sep 22, 2009, at 1:27 AM, John Wang <john.wang@gmail.com
> >     <mailto:john.wang@gmail.com>
> >     >>     <mailto:john.wang@gmail.com <mailto:john.wang@gmail.com>>>
> >     wrote:
> >     >>
> >     >>>     Hi Yonik:
> >     >>>
> >     >>>          Actually that is what I am looking for. Can you
> >     please point
> >     >>>     me to where/how sorting is done per-segment?
> >     >>>
> >     >>>          When heaving indexing introduces or modifies
> >     segments, would
> >     >>>     it cause reloading of FieldCache at query time and thus would
> >     >>>     impact search performance?
> >     >>>
> >     >>>     thanks
> >     >>>
> >     >>>     -John
> >     >>>
> >     >>>     On Tue, Sep 22, 2009 at 1:05 PM, Yonik Seeley
> >     >>>     <yonik@lucidimagination.com
> >     <mailto:yonik@lucidimagination.com>
> >     <mailto:yonik@lucidimagination.com
> >     <mailto:yonik@lucidimagination.com>>>
> >     >>>     wrote:
> >     >>>
> >     >>>     On Tue, Sep 22, 2009 at 12:56 AM, John Wang
> >     <john.wang@gmail.com <mailto:john.wang@gmail.com>
> >     >>>     <mailto:john.wang@gmail.com <mailto:john.wang@gmail.com>>>
> >     wrote:
> >     >>>     > Looking at the code, seems there is a disconnect between
> >     >>>     how/when field
> >     >>>     > cache is loaded when IndexWriter.getReader() is called.
> >     >>>
> >     >>>     I'm not sure what you mean by "disconnect"
> >     >>>
> >     >>>     > Is FieldCache updated?
> >     >>>
> >     >>>     FieldCache entries are populated on demand, as they always
> >     have been.
> >     >>>
> >     >>>
> >     >>>     > Otherwise, are we reloading FieldCache for each
> >     >>>     > reader instance?
> >     >>>
> >     >>>     Searching/sorting is now per-segment, and so is the use of
> the
> >     >>>     FieldCache.  Segments that don't change shouldn't have to
> >     reload
> >     >>>     their
> >     >>>     FieldCache entries.
> >     >>>
> >     >>>     -Yonik
> >     >>>     http://www.lucidimagination.com
> >     >>>
> >     >>>
> >     ---------------------------------------------------------------------
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> >     <mailto:java-dev-help@lucene.apache.org>>
> >     >>>
> >     >>>
> >     >>>
> >     >>
> >     >>
> >     >>
> >     >
> >     >
> >     > --
> >     > - Mark
> >     >
> >     > http://www.lucidimagination.com
> >     >
> >     >
> >     >
> >     >
> >     >
> >     ---------------------------------------------------------------------
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> >     >
> >     >
> >
> >     ---------------------------------------------------------------------
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> >
> >
>
>
> --
> - Mark
>
> http://www.lucidimagination.com
>
>
>
>
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