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From Mark Miller <markrmil...@gmail.com>
Subject Re: First search is slow after updating index .. subsequent searches very fast
Date Thu, 21 Dec 2006 20:48:20 GMT
Since you say you are sorting on a field the bulk of the time will be 
doing the sort and caching it (FieldCache). Subsequent searches use that 
cache to avoid paying the full sort cost again. If you where doing 
relevancy sorting you would not experience such a big delay.

- Mark

Bryan Dotzour wrote:
> Otis thanks for your suggestion, it seems to be working pretty well!
> I'm just curious if you (or anyone else) could describe what is actually
> happening during that initial query that ends up taking so much time.
> We have several different indexes for different types of objects and
> it's only this one index that exhibits this kind of behavior.  Is it
> something related to the size of the index, or the number of fields, or
> how fragmented the index is?
>
> I'm just trying to get a little better understanding of what is going on
> under the covers there.  I'll spend some time with the source to see if
> I can figure it out, but any tips from the experts would be much
> appreciated. =)
>
> Thanks again!
> Bryan
>
> -----Original Message-----
> From: Otis Gospodnetic [mailto:otis_gospodnetic@yahoo.com] 
> Sent: Wednesday, December 20, 2006 4:28 PM
> To: java-user@lucene.apache.org
> Subject: Re: First search is slow after updating index .. subsequent
> searches very fast
>
> To populate FieldCache, the number of matches doesn't matter.  There is
> no need to be scrimy there - you don't really save anything by running a
> query that matches only a few docs.  Just run something that looks like
> a common query.
>
> For warming up new indices, one can also use the `dd' trick under UNIX.
>
> Otis
>
> ----- Original Message ----
> From: Bryan Dotzour <BDotzour@widen.com>
> To: java-user@lucene.apache.org
> Sent: Wednesday, December 20, 2006 5:23:40 PM
> Subject: RE: First search is slow after updating index .. subsequent
> searches very fast
>
> One question about this, Otis... When "warming up" the new searcher,
> should the query return a lot of results, or does it matter?  Can I just
> do like an ID = X query and get one document back?  Is that sufficient
> or is it better to run a query that will get lots of hits?
>
> Thanks again,
> Bryan
>
> -----Original Message-----
> From: Otis Gospodnetic [mailto:otis_gospodnetic@yahoo.com] 
> Sent: Wednesday, December 20, 2006 3:28 PM
> To: java-user@lucene.apache.org
> Subject: Re: First search is slow after updating index .. subsequent
> searches very fast
>
> All sounds good.  Opening a new IndexReader can take a bit of time.  If
> you use sorting of any kind other than default sorting by relevance,
> this delay on the first search is also probably caused by the lazy
> FieldCache population.  The cure for that is to open a new
> IndexReader/Searcher before you close the old one, warm it up with a
> query + sort, and then switch IndexReader/Searchers, closing the old
> one.
>
> Otis
>
> ----- Original Message ----
> From: Bryan Dotzour <BDotzour@widen.com>
> To: java-user@lucene.apache.org
> Sent: Wednesday, December 20, 2006 3:59:19 PM
> Subject: First search is slow after updating index .. subsequent
> searches very fast
>
> I'm investigating some performance issues with the way we're using
> Lucene in our web app and am interested if anyone could shed some light
> on what might be going on.  Hopefully I can provide enough information,
> please let me know if there's more I can give.
>
>  
>
> We're using Lucene 2.0.0 and I'm currently working with disk-based
> indexing (although in production I'll want to be using RAM indexing).
> In our environment, we build up our Lucene index at application start up
> time and then we optimize the index.  From then on, updates and deletes
> to the index occur fairly frequently but we don't optimize until the
> middle of the night when the impact would be at its minimum.  After a
> while, what I see is that searches will be very fast (~400 ms) until I
> make a modification that will require a single document to be
> re-indexed.  Immediately after that has occurred, the next search will
> take substantially longer (sometimes up to ~25s).  After that search has
> run, the next search will be back at the ~400ms time.
>
>  
>
> Our algorithm for handling the updates is as follows:
>
> 1.       open an IndexReader on the directory
>
> 2.       delete the document using the reader
>
> 3.       close the reader
>
> 4.       open an IndexWriter
>
> 5.       add the new document using the writer
>
> 6.       close the writer
>
>  
>
> For searches:
>
> 1.    We cache off an IndexReader for the index, as well as an
> IndexSearcher, which uses that reader
> 2.    When a search is initiated we check to see if the version of the
> index has changed using getCurrentVersion()
> 3.    If it has changed, we close our IndexSearcher, close the
> IndexReader and re-open them both
>
>  
>
>  
>
> Anything sound non-standard in that workflow?  Does anyone have an idea
> of what might be happening during that slow down?
>
>  
>
> Thanks for your time,
>
> Bryan
>
>  
>
>  
>
>  
>
> (For a little more info, here is a very common stack trace snippet that
> I gather when the "slow search" is running.  It seems much of the time
> is spent in MultiReader or MultiTermDocs)
>
>  
> org.apache.lucene.index.CompoundFileReader$CSIndexInput.readInternal(Com
> poundFileReader.java:214)
>  
> org.apache.lucene.store.BufferedIndexInput.refill(BufferedIndexInput.jav
> a:64)
>  
> org.apache.lucene.store.BufferedIndexInput.readByte(BufferedIndexInput.j
> ava:33)
>       org.apache.lucene.store.IndexInput.readVInt(IndexInput.java:56)
>       org.apache.lucene.index.TermBuffer.read(TermBuffer.java:62)
>  
> org.apache.lucene.index.SegmentTermEnum.next(SegmentTermEnum.java:117)
>  
> org.apache.lucene.index.SegmentTermEnum.scanTo(SegmentTermEnum.java:148)
>  
> org.apache.lucene.index.TermInfosReader.scanEnum(TermInfosReader.java:15
> 7)
>  
> org.apache.lucene.index.TermInfosReader.get(TermInfosReader.java:151)
>  
> org.apache.lucene.index.SegmentTermDocs.seek(SegmentTermDocs.java:50)
>  
> org.apache.lucene.index.MultiTermDocs.termDocs(MultiReader.java:392)
>       org.apache.lucene.index.MultiTermDocs.next(MultiReader.java:348)
>       org.apache.lucene.index.MultiTermDocs.next(MultiReader.java:349)
>       org.apache.lucene.index.MultiTermDocs.next(MultiReader.java:349)
>       org.apache.lucene.index.MultiTermDocs.next(MultiReader.java:349)
>  
> org.apache.lucene.search.FieldCacheImpl.getInts(FieldCacheImpl.java:171)
>  
> org.apache.lucene.search.FieldCacheImpl.getInts(FieldCacheImpl.java:153)
>  
> org.apache.lucene.search.FieldCacheImpl.getAuto(FieldCacheImpl.java:349)
>  
> org.apache.lucene.search.FieldSortedHitQueue.comparatorAuto(FieldSortedH
> itQueue.java:346)
>  
> org.apache.lucene.search.FieldSortedHitQueue.getCachedComparator(FieldSo
> rtedHitQueue.java:189)
>  
> org.apache.lucene.search.FieldSortedHitQueue.(FieldSortedHitQueue.java:5
> 8)
>  
> org.apache.lucene.search.TopFieldDocCollector.(TopFieldDocCollector.java
> :40)
>  
> org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:108)
>       org.apache.lucene.search.Hits.getMoreDocs(Hits.java:65)
>       org.apache.lucene.search.Hits.(Hits.java:52)
>       org.apache.lucene.search.Searcher.search(Searcher.java:53)
>
>  
>
>
>
>
>
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