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expand_keywords
Expand keywords with exact forms and/or stars when possible. Optional, default is 0 (do not expand keywords). Introduced in version 1.10-beta.
Queries against indexes with expand_keywords feature
enabled are internally expanded as follows. If the index was built with
prefix or infix indexing enabled, every keyword gets internally replaced
with a disjunction of keyword itself and a respective prefix or infix
(keyword with stars). If the index was built with both stemming and
index_exact_words enabled,
exact form is also added. Here's an example that shows how internal
expansion works when all of the above (infixes, stemming, and exact
words) are combined:
running -> ( running | *running* | =running )
Expanded queries take naturally longer to complete, but can possibly improve the search quality, as the documents with exact form matches should be ranked generally higher than documents with stemmed or infix matches.
Note that the existing query syntax does not allow to emulate this kind of expansion, because internal expansion works on keyword level and expands keywords within phrase or quorum operators too (which is not possible through the query syntax).
This directive does not affect indexer in any way,
it only affects searchd.
Example:
expand_keywords = 1
