[ http://issues.apache.org/jira/browse/LUCENE-505?page=comments#action_12368443 ]
Steven Tamm commented on LUCENE-505: ------------------------------------ We're still using TermScorer, which generates the fakeNorms() regardless of omitNorms on or off. ConstantTermScorer is a step in the right direction, but you already said what I was going to say about it . Specifically, we have one field where we want norms, and one field where we don't. As you can see by the "LazyNorms" patch, the big bang for the buck for us (besides optimizing TermScorer.score()), was to lazily load the norms from the disk since we don't keep the indexes in memory. If you only are scoring 3 docs (ever), why should it load a 1MB array (or in the case of TermScorer, a 1MB array from disk and then an empty 1MB array). A better ConstantScoreQuery would also work, but only if the caller knew which fields had omitNorms on or off. > MultiReader.norm() takes up too much memory: norms byte[] should be made into > an Object > --------------------------------------------------------------------------------------- > > Key: LUCENE-505 > URL: http://issues.apache.org/jira/browse/LUCENE-505 > Project: Lucene - Java > Type: Improvement > Components: Index > Versions: 2.0 > Environment: Patch is against Lucene 1.9 trunk (as of Mar 1 06) > Reporter: Steven Tamm > Attachments: LazyNorms.patch, NormFactors.patch, NormFactors.patch > > MultiReader.norms() is very inefficient: it has to construct a byte array > that's as long as all the documents in every segment. This doubles the > memory requirement for scoring MultiReaders vs. Segment Readers. Although > this is cached, it's still a baseline of memory that is unnecessary. > The problem is that the Normalization Factors are passed around as a byte[]. > If it were instead replaced with an Object, you could perform a whole host of > optimizations > a. When reading, you wouldn't have to construct a "fakeNorms" array of all > 1.0fs. You could instead return a singleton object that would just return > 1.0f. > b. MultiReader could use an object that could delegate to NormFactors of the > subreaders > c. You could write an implementation that could use mmap to access the norm > factors. Or if the index isn't long lived, you could use an implementation > that reads directly from the disk. > The patch provided here replaces the use of byte[] with a new abstract class > called NormFactors. > NormFactors has two methods on it > public abstract byte getByte(int doc) throws IOException; // Returns the > byte[doc] > public float getFactor(int doc) throws IOException; // Calls > Similarity.decodeNorm(getByte(doc)) > There are four implementations of this abstract class > 1. NormFactors.EmptyNormFactors - This replaces the fakeNorms with a > singleton that only returns 1.0 > 2. NormFactors.ByteNormFactors - Converts a byte[] to a NormFactors for > backwards compatibility in constructors. > 3. MultiNormFactors - Multiplexes the NormFactors in MultiReader to prevent > the need to construct the gigantic norms array. > 4. SegmentReader.Norm - Same class, but now extends NormFactors to provide > the same access. > In addition, Many of the Query and Scorer classes were changes to pass around > NormFactors instead of byte[], and to call getFactor() instead of using the > byte[]. I have kept around IndexReader.norms(String) for backwards > compatibiltiy, but marked it as deprecated. I believe that the use of > ByteNormFactors in IndexReader.getNormFactors() will keep backward > compatibility with other IndexReader implementations, but I don't know how to > test that. -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
