When performing queries across multiple indexes, it is sometimes desirable to
target indexes held on nodes of a given data tier (
_tier field allows matching on the
tier_preference setting of the index a document was indexed into.
The preferred value is accessible in certain queries :
Typically a query will use a
terms query to list the tiers of interest but you can use
_tier field in any query that is rewritten to a
term query, such as the
simple_query_string query, as well as
wildcard queries. However, it does not support
tier_preference setting of the index is a comma-delimited list of tier names
in order of preference i.e. the preferred tier for hosting an index is listed first followed
by potentially many fall-back options. Query matching only considers the first preference
(the first value of a list).