The `min` and `max` sort modes are supported for all field types. Either the lowest value or the highest value is picked. In addition to that number based fields also support `sum` and `avg` as sort mode. If `sum` sort mode is used then all the values for a field and belonging to a document are added together and the result of that is used as sort value. If the `avg` sort mode is used then the average of all values for the sort field belonging to that document is used as sort value.
Relates to #2634
The rescore feature allows te rescore a document returned by a query based
on a secondary algorithm. Rescoring is commonly used if a scoring algorithm
is too costly to be executed across the entire document set but efficient enough
to be executed on the Top-K documents scored by a faster retrieval method. Rescoring
can help to improve precision by reordering a larger Top-K window than actually
returned to the user. Typically is it executed on a window between 100 and 500 documents
while the actual result window requested by the user remains the same.
# Query Rescorer
The `query` rescorer executes a secondary query only on the Top-K results of the actual
user query and rescores the documents based on a linear combination of the user query's score
and the score of the `rescore_query`. This allows to execute any exposed query as a
`rescore_query` and supports a `query_weight` as well as a `rescore_query_weight` to weight the
factors of the linear combination.
# Rescore API
The `rescore` request is defined along side the query part in the json request:
```json
curl -s -XPOST 'localhost:9200/_search' -d {
"query" : {
"match" : {
"field1" : {
"query" : "the quick brown",
"type" : "boolean",
"operator" : "OR"
}
}
},
"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
}
}
}
```
Each `rescore` request is executed on a per-shard basis within the same roundtrip. Currently the rescore API
has only one implementation (the `query` rescorer) which modifies the result set in-place. Future developments
could include dedicated rescore results if needed by the implemenation ie. a pair-wise reranker.
*Note:* Only regualr queries are rescored, if the search type is set to `scan` or `count` rescorers are not executed.
Closes#2640
Stats, histogram and range facets and sorting currently fail if a field that they are running on is not defined in the mapping. In case of dynamic fields it might mean that by the time the facet query is executed the new field mapping might not be propagated to all nodes yet.
When startNode exits there is no guarantee that shard cleanup is finished because the cleanup operation is performed on another thread and startNode doesn't wait for it to complete. Therefore we might need to wait for the shard to disappear.
Igor Motov
Shay Banon
Martijn van Groningen
Simon Willnauer
morsegel
uboness
Lee Hinman
Florian Schilling