title: DynamoDB - Data model for geohash and frequent updates
body: <p>I'm build a location based "chat" application and am using Amazon's DynamoDB to take advantage of the high throughput and automatic scaling.</p>
  
  <p>The application will frequently update user's location's in the database (I'm using a PHP geohash library). It will also search for users within a specific geographic radius.  </p>
  
  <p>I'm new to NoSQL (I have a lot of MySQL experience) and would like some input on modeling my "Users" table. Two concerns:</p>
  
  <p>1) If the geohash / longitude / latitude attributes of users are updated frequently, will this cause an issue (table locking?) with DynamoDB?  In MySQL, I would create a separate table for just those values to prevent locking the entire Users table.  Do I need to worry about that in DynamoDB?</p>
  
  <p>2) Searching for users in a geographic radius?  Is this just setting up a Global Secondary Index on the geohash attribute and performing a query on that?  Will sharding cause an issue with this?</p>