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From "Carl Austin (JIRA)" <>
Subject [jira] Commented: (LUCENE-1690) Morelikethis queries are very slow compared to other search types
Date Thu, 30 Jul 2009 13:57:14 GMT


Carl Austin commented on LUCENE-1690:

The cache in terminfosreader is for everything as you say. I do a lot of stuff with terms,
and those terms will get pushed out of this LRU cache very quickly. 
I have a separate cache on my version of the MLT. This has the advantage of those terms only
being pushed out by other MLT queries, and not by everything else I am doing that is not MLT
A lot of MLTs use the same terms, and I have a good size cache for it, meaning most terms
I use in MLT can be retrieved from there. Seeing as MLT in my circumstance is one of the slower
bits, this can give me a good advantage.

> Morelikethis queries are very slow compared to other search types
> -----------------------------------------------------------------
>                 Key: LUCENE-1690
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: contrib/*
>    Affects Versions: 2.4.1
>            Reporter: Richard Marr
>            Priority: Minor
>         Attachments: LruCache.patch, LUCENE-1690.patch, LUCENE-1690.patch
>   Original Estimate: 2h
>  Remaining Estimate: 2h
> The MoreLikeThis object performs term frequency lookups for every query.  From my testing
that's what seems to take up the majority of time for MoreLikeThis searches.  
> For some (I'd venture many) applications it's not necessary for term statistics to be
looked up every time. A fairly naive opt-in caching mechanism tied to the life of the MoreLikeThis
object would allow applications to cache term statistics for the duration that suits them.
> I've got this working in my test code. I'll put together a patch file when I get a minute.
From my testing this can improve performance by a factor of around 10.

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