As we mentioned in Chapter 1, Introduction to Efficient Indexing, understanding the difference between storable and searchable fields is important for indexing performance and relevant search results. Elasticsearch always stores every document field within the _source field by default. You can change this behavior for some fields that are not really needed to be return. It provides indexing performance and reduces your storage costs.
Also, as we mentioned in Chapter 5, Anatomy of an Elasticsearch Cluster, shards and the number of replicas affect the indexing speed. For example, having more shards provides faster indexing. Therefore, every operation executed on a smaller index will be faster.
