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Rescoringedit
Rescoring can help to improve precision by reordering just the top (eg
100 - 500) documents returned by the
query and
post_filter phases, using a
secondary (usually more costly) algorithm, instead of applying the
costly algorithm to all documents in the index.
A rescore request is executed on each shard before it returns its
results to be sorted by the node handling the overall search request.
Currently the rescore API has only one implementation: the query rescorer, which uses a query to tweak the scoring. In the future, alternative rescorers may be made available, for example, a pair-wise rescorer.
Note: the rescore phase is not executed when
search_type is set
to scan or count.
Query rescoreredit
The query rescorer executes a second query only on the Top-K results
returned by the query and
post_filter phases. The
number of docs which will be examined on each shard can be controlled by
the window_size parameter, which defaults to
from and size.
The scores from the original query and the rescore query are combined
linearly to produce the final _score for each document. The relative
importance of the original query and of the rescore query can be
controlled with the query_weight and rescore_query_weight
respectively. Both default to 1.
For example:
curl -s -XPOST 'localhost:9200/_search' -d '{
"query" : {
"match" : {
"field1" : {
"operator" : "or",
"query" : "the quick brown",
"type" : "boolean"
}
}
},
"rescore" : {
"window_size" : 50,
"query" : {
"rescore_query" : {
"match" : {
"field1" : {
"query" : "the quick brown",
"type" : "phrase",
"slop" : 2
}
}
},
"query_weight" : 0.7,
"rescore_query_weight" : 1.2
}
}
}
'