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81 lines
3.6 KiB
Plaintext
81 lines
3.6 KiB
Plaintext
# Apache Lucene Migration Guide
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## The way how number of document calculated is changed (LUCENE-6711)
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The number of documents (numDocs) is used to calculate term specificity (idf) and average document length (avdl).
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Prior to LUCENE-6711, collectionStats.maxDoc() was used for the statistics.
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Now, collectionStats.docCount() is used whenever possible, if not maxDocs() is used.
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Assume that a collection contains 100 documents, and 50 of them have "keywords" field.
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In this example, maxDocs is 100 while docCount is 50 for the "keywords" field.
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The total number of tokens for "keywords" field is divided by docCount to obtain avdl.
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Therefore, docCount which is the total number of documents that have at least one term for the field, is a more precise metric for optional fields.
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DefaultSimilarity does not leverage avdl, so this change would have relatively minor change in the result list.
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Because relative idf values of terms will remain same.
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However, when combined with other factors such as term frequency, relative ranking of documents could change.
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Some Similarity implementations (such as the ones instantiated with NormalizationH2 and BM25) take account into avdl and would have notable change in ranked list.
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Especially if you have a collection of documents with varying lengths.
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Because NormalizationH2 tends to punish documents longer than avdl.
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## Separation of IndexDocument and StoredDocument (LUCENE-3312)
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The API of oal.document was restructured to differentiate between stored
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documents and indexed documents. IndexReader.document(int) now returns
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StoredDocument instead of Document. In most cases a simple replacement
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of the return type is enough to upgrade.
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## FunctionValues.exist() Behavior Changes due to ValueSource bug fixes (LUCENE-5961)
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Bugs fixed in several ValueSource functions may result in different behavior in
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situations where some documents do not have values for fields wrapped in other
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ValueSources. Users who want to preserve the previous behavior may need to wrap
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their ValueSources in a "DefFunction" along with a ConstValueSource of "0.0".
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## Removal of FilteredQuery (LUCENE-6583)
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FilteredQuery has been removed. Instead, you can construct a BooleanQuery with
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one MUST clause for the query, and one FILTER clause for the filter.
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## PhraseQuery and BooleanQuery made immutable (LUCENE-6531 LUCENE-6570)
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PhraseQuery and BooleanQuery are now immutable and have a builder API to help
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construct them. For instance a BooleanQuery that used to be constructed like
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this:
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BooleanQuery bq = new BooleanQuery();
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bq.add(q1, Occur.SHOULD);
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bq.add(q2, Occur.SHOULD);
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bq.add(q3, Occur.MUST);
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bq.setMinimumNumberShouldMatch(1);
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can now be constructed this way using its builder:
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BooleanQuery bq = new BooleanQuery.Builder()
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.add(q1, Occur.SHOULD)
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.add(q2, Occur.SHOULD)
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.add(q3, Occur.SHOULD)
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.setMinimumNumberShouldMatch(1)
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.build();
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## AttributeImpl now requires that reflectWith() is implemented (LUCENE-6651)
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AttributeImpl removed the default, reflection-based implementation of
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reflectWith(AtrributeReflector). The method was made abstract. If you have
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implemented your own attribute, make sure to add the required method sigature.
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See the Javadocs for an example.
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## Query.setBoost() and Query.clone() are removed (LUCENE-6590)
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Query.setBoost has been removed. In order to apply a boost to a Query, you now
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need to wrap it inside a BoostQuery. For instance,
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Query q = ...;
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float boost = ...;
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q = new BoostQuery(q, boost);
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would be equivalent to the following code with the old setBoost API:
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Query q = ...;
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float boost = ...;
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q.setBoost(q.getBoost() * boost);
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