code: func (r *SearchRequest) PreFilterShardSize(size int) *SearchRequest {
  	r.preFilterShardSize = &size
  	return r
  }
docs: // PreFilterShardSize sets a threshold that enforces a pre-filter roundtrip
  // to pre-filter search shards based on query rewriting if the number of
  // shards the search request expands to exceeds the threshold.
  // This filter roundtrip can limit the number of shards significantly if for
  // instance a shard can not match any documents based on it's rewrite
  // method ie. if date filters are mandatory to match but the shard
  // bounds and the query are disjoint. The default is 128.