Atomic updates allow you to update an already indexed document by giving a new field value, adding a value to the existing values on a multivalued field, or by incrementing a numeric field. Instead of giving an entire document, you supply a document that only has the fields that are to be modified in some way, and with a special modifier (described next). If Solr sees these modifiers on any field in an incoming document, then it knows this is an atomic-update to an existing document versus a new or replacement document. This is both a convenience feature, and with optimistic concurrency (described soon), allows Solr to be a credible NoSQL option.

We'll show you how this is used by way of a succinct example, and we'll use JSON this time. Note that, most fields don't just have a value but are structured to include one of several mutation modifiers. In the XML syntax, these are specified with attributes.

{"id":"mydoc",
 "price":{"set":99},
 "popularity...