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Docs fix- added performance note about plain highlighter 

Closes #11442
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markharwood 2015-07-15 10:49:48 +01:00
parent f8ba89d9e4
commit 52fb3c3a09
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docs/reference/search/request/highlighting.asciidoc
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@ -37,6 +37,18 @@ be used for highlighting if it mapped to have `store` set to `true`.
The field name supports wildcard notation. For example, using `comment_*`
will cause all fields that match the expression to be highlighted.
[[plain-highlighter]]
==== Plain highlighter
The default choice of highlighter is of type `plain` and uses the Lucene highlighter.
It tries hard to reflect the query matching logic in terms of understanding word importance and any word positioning criteria in phrase queries.
[WARNING]
If you want to highlight a lot of fields in a lot of documents with complex queries this highlighter will not be fast.
In its efforts to accurately reflect query logic 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 the current document.
This is repeated for every field and every document that needs highlighting. If this presents a performance issue in your system consider using an alternative highlighter.
[[postings-highlighter]]
==== Postings highlighter