6.3 added a new allow_partial_search_results flag to control behaviour when there are partial results. This was documented in the query-request docs but the equivalent cluster-level setting (search.default_allow_partial_results) is currently undocumented.

We don't currently have a page for "search" cluster settings such as search.max_buckets and these settings tend to get mentioned elsewhere. Following suit, I plan to add a note in the docs/reference/search/uri-request.asciidoc and docs/reference/search/request-body.asciidoc docs about the cluster-level setting.