title: Performance of Cloud Bigtable row counts
body: <p>I'd like to gauge Cloud Bigtable's performance at grabbing many row counts of keys with certain prefixes.</p>
  
  <p>Say a schema has row keys with unix timestamp at the end, e.g., <code>event_id#unix_timestamp</code>.</p>
  
  <p>If I needed to grab the total number of rows for each of 20 different event_id's, is Cloud Bigtable efficient at doing this? I'd either use a prefix or a row range query to do this.</p>