Add a new cluster setting `search.allow_expensive_queries` which by
default is `true`. If set to `false`, certain queries that have
usually slow performance cannot be executed and an error message
is returned.
- Queries that need to do linear scans to identify matches:
- Script queries
- Queries that have a high up-front cost:
- Fuzzy queries
- Regexp queries
- Prefix queries (without index_prefixes enabled
- Wildcard queries
- Range queries on text and keyword fields
- Joining queries
- HasParent queries
- HasChild queries
- ParentId queries
- Nested queries
- Queries on deprecated 6.x geo shapes (using PrefixTree implementation)
- Queries that may have a high per-document cost:
- Script score queries
- Percolate queries
Closes: #29050
(cherry picked from commit a8b39ed842c7770bd9275958c9f747502fd9a3ea)
* Remove remaining 1.x bwc logic.
* Stop storing stored fields and indexed terms. The _parent field's only purpose is to support joins between parent and child type and only storing doc values is sufficient.
* In the mapping the parent field mapper is now known under '{parent}#{child}' key, because this is the field the parent/child join uses too.
* Added new sub fetch phase to lookup that _parent field from doc values field if that is required (before this was fetched from stored _parent field)
* Removed the ability to query directly on `_parent` in the query dsl. Instead the `{parent}#{child}` field should be used. Under the hood a doc values query is used instead of a term query, because only doc values fields are stored now.
* Added a new `parent_id` query to easily query child documents with a specific parent id without having to know what join field to use
* Also in aggregations `_parent` field can't be used any more and `{parent}#{child}` field name should be used instead to aggregate directly on the _parent join field.
Marios Trivyzas
James Rodewig
Clinton Gormley
Anatolii Stepaniuk
Martijn van Groningen