Avoid overloading default search type to dfs_query_then_fetch?

[jtibshirani]

Unless it's specified, the search type is set to dfs_query_then_fetch:

spring-data-elasticsearch/src/main/java/org/springframework/data/elasticsearch/core/query/AbstractQuery.java

Line 55 in d80d920

protected SearchType searchType = SearchType.DFS_QUERY_THEN_FETCH;

The default search type in Elasticsearch itself is query_then_fetch. Compared to this Elasticsearch default, dfs_query_then_fetch performs an extra round trip to the nodes before starting the main search to gather term frequency information. In general, the dfs_query_then_fetch type is only used in special situations where exact text scoring is important.

To avoid adding the extra roundtrip, AbstractQuery could fall back to the Elasticsearch default instead of setting dfs_query_then_fetch.

[sothawo]

Thanks for finding this. That value has been in there since this property was added in Spring Data Elasticsearch back in march 2014 - nowadays nobody knows why it was set to this value then.

This will be cleaned up together with the changes of #1885