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From Jason Rutherglen <jason.rutherg...@gmail.com>
Subject Re: How to leverage the LogMergePolicy "calibrateSizeByDeletes" patch in Solr ?
Date Tue, 22 Sep 2009 18:48:46 GMT
For that you can subclass IW.mergeSuccess.

On Tue, Sep 22, 2009 at 11:43 AM, Tim Smith <tsmith@attivio.com> wrote:
> Jason Rutherglen wrote:
>
> I have a working version of Simple FieldCache Merging LUCENE-1785 that
> should go in real soon.
>
>
>
> Will this contain a callback mechanism i can register with to know what
> segments are being merged?
> that way i can merge my own caches as well at the application layer, perhaps
> exposed through something like IndexReaderWarmer.warmMerge(IndexReader[]
> input, IndexReader output)
>
> On Tue, Sep 22, 2009 at 11:14 AM, Mark Miller <markrmiller@gmail.com> wrote:
>
>
> 1. see IndexWriter and the method/class that Mike pointed out earlier
> for the warming.
>
> 2. See Lucene-831 - I think we will get some form of that in someday.
>
> Tim Smith wrote:
>
>
> This sounds pretty interesting
>
> is there a proposed API for doing this warming yet?
> Is there a ticket tracking this?
>
> for my use cases, it would be really nice for applications to be able
> to associate a custom "IndexCache" object with an index reader, then
> this pluggable "AutoWarmer" would be in charge of initializing this
> cache for a segment reader. I have a number of caches outside the
> realm of regular field caches that i associate with a segment,
> currently doing this after getting the IndexReader by iterating over
> its segments, and getting a cache object shared across all instances
> of the same logical segment. it would be nice if i could just have my
> "cache" object subclass a lucene IndexCache class and drop it right
> into this auto warming infrastructure (would greatly simplify things).
>
> then, once the index reader has been closed, it would call close on
> any attached IndexCache objects in order to free up memory/objects.
> (so i don't have to maintain reference counts anymore)
>
> Seems this could also greatly simplify the current field caching
> mechanisms, as the field caches could be associated with an
> IndexReader directly using the attached "IndexCache" object, instead
> of using static weak reference hash maps. (could then add methods like
> getFieldCache() to the IndexReader)
>
>  -- Tim Smith
>
> Michael McCandless wrote:
>
>
> Well described, that's exactly it!  I like the concrete example :)
>
> Thanks Yonik.
>
> Mike
>
> On Tue, Sep 22, 2009 at 1:38 PM, Yonik Seeley
> <yonik@lucidimagination.com> wrote:
>
>
>
> OK Mike, thanks for your patience - I understand now :-)
>
> Here's an example that helped me understand - hopefully it will add to
> others understanding more than it confuses ;-)
>
> IW.getReader() => segments={A, B}
>  // something causes a merge of A,B into AB to start
> addDoc(doc1)
>  // doc1 goes into segment C
> IW.getReader() => segments={A, B, C}
>  // merge isn't done yet, so getReader() still returns A,B instead of
> AB, but doc1 is still searchable!
>
> OK, in this scenario, there's no advantage to warming in the IW vs the app.
> Let's start over with a little different timing:
>
> segments={A,B}
>  // something causes a merge of A,B into AB to start
> addDoc(doc1)
>  // doc1 goes into segment C
>  // merging of A,B into AB finishes
> IW.getReader() => segments={AB, C}
>
> Oh, no... with warming at the app level, we need to warm the huge AB
> segment before doc1 is visible.  We could continue using the old
> reader while the warming is ongoing, so no user requests will
> experience long queries, but doc1 isn't in the old segment.
>
> With warming in the IW (basically warming becomes part of the same
> operation as merging), then getReader() would return segments={A,B,C}
> and doc1 would still be instantly searchable.
>
> The only way to duplicate this functionality at the app layer would be
> to recognize that there is a new segment, try and figure out what old
> segments were merged to create this new segment, and create a reader
> that's a mix of old and new to avoid unwarmed segments - not nice.
>
> -Yonik
> http://www.lucidimagination.com
>
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