[ElasticSearch] 자꾸 까먹어..ㅡ.ㅡ;; (preference)

http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-request-preference.html

preference

Controls a preference of which shard replicas to execute the search request on. By default, the operation is randomized between the shard replicas.

The preference is a query string parameter which can be set to:

_primary	The operation will go and be executed only on the primary  shards.
_primary_first	The operation will go and be executed on the primary shard, and if not available (failover), will execute on other shards.
_local	The operation will prefer to be executed on a local allocated shard if possible.
_only_node:xyz	Restricts the search to execute only on a node with the provided node id (xyz in this case).
_prefer_node:xyz	Prefers execution on the node with the provided node id (xyz in this case) if applicable.
_shards:2,3	Restricts the operation to the specified shards. (2 and 3  in this case). This preference can be combined with other preferences but it has to appear first: _shards:2,3;_primary
Custom (string) value	A custom value will be used to guarantee that the same shards will be used for the same custom value. This can help with "jumping values" when hitting different shards in different refresh states. A sample value can be something like the web session id, or the user name.