109 lines
4.2 KiB
Plaintext
109 lines
4.2 KiB
Plaintext
[[query-dsl-multi-term-rewrite]]
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== `rewrite` parameter
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WARNING: This parameter is for expert users only. Changing the value of
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this parameter can impact search performance and relevance.
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{es} uses https://lucene.apache.org/core/[Apache Lucene] internally to power
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indexing and searching. In their original form, Lucene cannot execute the
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following queries:
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* <<query-dsl-fuzzy-query, `fuzzy`>>
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* <<query-dsl-prefix-query, `prefix`>>
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* <<query-dsl-query-string-query, `query_string`>>
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* <<query-dsl-regexp-query, `regexp`>>
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* <<query-dsl-wildcard-query, `wildcard`>>
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To execute them, Lucene changes these queries to a simpler form, such as a
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<<query-dsl-bool-query, `bool` query>> or a
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{wikipedia}/Bit_array[bit set].
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The `rewrite` parameter determines:
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* How Lucene calculates the relevance scores for each matching document
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* Whether Lucene changes the original query to a `bool`
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query or bit set
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* If changed to a `bool` query, which `term` query clauses are included
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[discrete]
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[[rewrite-param-valid-values]]
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=== Valid values
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`constant_score` (Default)::
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Uses the `constant_score_boolean` method for fewer matching terms. Otherwise,
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this method finds all matching terms in sequence and returns matching documents
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using a bit set.
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`constant_score_boolean`::
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Assigns each document a relevance score equal to the `boost`
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parameter.
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+
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This method changes the original query to a <<query-dsl-bool-query, `bool`
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query>>. This `bool` query contains a `should` clause and
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<<query-dsl-term-query, `term` query>> for each matching term.
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+
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This method can cause the final `bool` query to exceed the clause limit in the
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<<indices-query-bool-max-clause-count, `indices.query.bool.max_clause_count`>>
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setting. If the query exceeds this limit, {es} returns an error.
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`scoring_boolean`::
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Calculates a relevance score for each matching document.
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+
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This method changes the original query to a <<query-dsl-bool-query, `bool`
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query>>. This `bool` query contains a `should` clause and
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<<query-dsl-term-query, `term` query>> for each matching term.
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+
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This method can cause the final `bool` query to exceed the clause limit in the
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<<indices-query-bool-max-clause-count, `indices.query.bool.max_clause_count`>>
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setting. If the query exceeds this limit, {es} returns an error.
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`top_terms_blended_freqs_N`::
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Calculates a relevance score for each matching document as if all terms had the
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same frequency. This frequency is the maximum frequency of all matching terms.
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+
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This method changes the original query to a <<query-dsl-bool-query, `bool`
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query>>. This `bool` query contains a `should` clause and
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<<query-dsl-term-query, `term` query>> for each matching term.
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+
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The final `bool` query only includes `term` queries for the top `N` scoring
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terms.
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+
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You can use this method to avoid exceeding the clause limit in the
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<<indices-query-bool-max-clause-count, `indices.query.bool.max_clause_count`>>
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setting.
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`top_terms_boost_N`::
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Assigns each matching document a relevance score equal to the `boost` parameter.
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+
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This method changes the original query to a <<query-dsl-bool-query, `bool`
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query>>. This `bool` query contains a `should` clause and
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<<query-dsl-term-query, `term` query>> for each matching term.
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+
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The final `bool` query only includes `term` queries for the top `N` terms.
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+
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You can use this method to avoid exceeding the clause limit in the
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<<indices-query-bool-max-clause-count, `indices.query.bool.max_clause_count`>>
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setting.
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`top_terms_N`::
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Calculates a relevance score for each matching document.
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+
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This method changes the original query to a <<query-dsl-bool-query, `bool`
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query>>. This `bool` query contains a `should` clause and
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<<query-dsl-term-query, `term` query>> for each matching term.
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+
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The final `bool` query
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only includes `term` queries for the top `N` scoring terms.
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+
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You can use this method to avoid exceeding the clause limit in the
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<<indices-query-bool-max-clause-count, `indices.query.bool.max_clause_count`>>
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setting.
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[discrete]
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[[rewrite-param-perf-considerations]]
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=== Performance considerations for the `rewrite` parameter
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For most uses, we recommend using the `constant_score`,
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`constant_score_boolean`, or `top_terms_boost_N` rewrite methods.
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Other methods calculate relevance scores. These score calculations are often
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expensive and do not improve query results. |