Controls a preference of which shard replicas to execute the search request on.
By default, the operation is randomized between the shard replicas.
The operation will go and be executed only on the primary shards.
The operation will go and be executed on the primary shard,
and if not available (failover), will execute on other shards.
The operation will go and be executed only on a replica shard.
The operation will go and be executed only on a replica shard, and if not available (failover), will execute on other shards.
The operation will prefer to be executed on a local allocated shard if possible.
Prefers execution on the nodes with the provided node ids (abc or xyz in this case) if applicable.
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
Restricts the operation to nodes specified in node specification
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.