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More clarifications on the unified highlighter being the new default (#25668) 

* More clarifications on the unified highlighter being the new default
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Jim Ferenczi 2017-07-13 15:38:58 +02:00 committed by GitHub
parent 13da3eb53e
commit fe383b7c27
1 changed files with 6 additions and 8 deletions
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docs/reference/search/request/highlighting.asciidoc
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@ -60,7 +60,7 @@ index and re-runs the original query criteria through Lucene's query execution
planner to get access to low-level match information for the current document. planner to get access to low-level match information for the current document.
This is repeated for every field and every document that needs to be highlighted. This is repeated for every field and every document that needs to be highlighted.
If you want to highlight a lot of fields in a lot of documents with complex If you want to highlight a lot of fields in a lot of documents with complex
queries, we recommend using one of the other highlighters. queries, we recommend using the `unified` highlighter on `postings` or `term_vector` fields.
[[fast-vector-highlighter]] [[fast-vector-highlighter]]
==== Fast vector highlighter ==== Fast vector highlighter
@ -68,8 +68,7 @@ The `fvh` highlighter uses the Lucene Fast Vector highlighter.
This highlighter can be used on fields with `term_vector` set to This highlighter can be used on fields with `term_vector` set to
`with_positions_offsets` in the mapping. The fast vector highlighter: `with_positions_offsets` in the mapping. The fast vector highlighter:
* Is faster especially for large fields (> `1MB`) * Can be customized with a <<boundary-scanners,`boundary_scanner`>>.
* Can be customized with a <<boundary-scanners,`boundary_scanner`>>.
* Requires setting `term_vector` to `with_positions_offsets` which * Requires setting `term_vector` to `with_positions_offsets` which
increases the size of the index increases the size of the index
* Can combine matches from multiple fields into one result. See * Can combine matches from multiple fields into one result. See
@ -95,12 +94,11 @@ disk space than using `term_vectors`.
* Term vectors. If `term_vector` information is provided by setting * Term vectors. If `term_vector` information is provided by setting
`term_vector` to `with_positions_offsets` in the mapping, the `unified` `term_vector` to `with_positions_offsets` in the mapping, the `unified`
highlighter automatically uses the `term_vector` to highlight the field. highlighter automatically uses the `term_vector` to highlight the field.
Term vector highlighting is faster for highlighting multi-term queries like It's fast especially for large fields (> `1MB`) and for highlighting multi-term queries like
`prefix` or `wildcard` because it can access the dictionary of terms for `prefix` or `wildcard` because it can access the dictionary of terms for each document.
each document, but it can be slower than using the postings list. The `fvh` The `fvh` highlighter always uses term vectors.
highlighter always uses term vectors.
* Plain highlighting. This mode is used when there is no other alternative. * Plain highlighting. This mode is used by the `unified` when there is no other alternative.
It creates a tiny in-memory index and re-runs the original query criteria through It creates a tiny in-memory index and re-runs the original query criteria through
Lucene's query execution planner to get access to low-level match information on Lucene's query execution planner to get access to low-level match information on
the current document. This is repeated for every field and every document that the current document. This is repeated for every field and every document that