count provides quick access to the document count of the entire
cluster, or individual indices.
GET /_cat/count?v
Looks like:
epoch timestamp count 1475868259 15:24:19 121
Or for a single index:
GET /_cat/count/twitter?v
epoch timestamp count 1475868259 15:24:20 120
The document count indicates the number of live documents and does not include deleted documents which have not yet been cleaned up by the merge process.