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Date: Wed, 14 Mar 2007 11:15:06 -0700 (PDT)
From: Chris Hostetter <hossman_lucene@fucit.org>
To: java-user@lucene.apache.org
Subject: Re: Performance between Filter and HitCollector?
In-Reply-To: <45F62B04.1050702@teamware.com>
Message-ID: <Pine.LNX.4.58.0703141103500.23841@hal.rescomp.berkeley.edu>
References: <45F62B04.1050702@teamware.com>
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it's kind of an Apples/Oranges comparison .. in the examples you gave
below, one is executing an arbitrary query (which oculd be anything) the
other is doing a simple TermEnumeration.

Asuming that Query is a TermQuery, the Filter is theoreticaly going to be
faster becuase it does't have to compute any Scores ... generally speaking
a a Filter will alwyas be a little faster then a functionally equivilent
Query for the purposes of building up a simple BitSet of matching
documents because teh Query involves the score calcuations ... but the
Query is generally more usable.

The Query can also be more efficient in other ways, because the
HitCollector doesn't *have* to build a BitSet, it can deal with the
results in whatever way it wants (where as a Filter allways generates a
BitSet).

Solr goes the HitCollector route for a few reasons:
  1) allows us to use hte DocSet abstraction which allows other
     performance benefits over straight BitSets
  2) allows us to have simpler code that builds DocSets and DocLists
     (DocLists know about scores, sorting, and pagination) in a single
     pass when scores or sorting are requested.


-Hoss


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