title: Aurora Replica Lag Much Higher Than Reported
body: <p>Our application uses reader and writer instances of Amazon RDS Aurora. The AWS dashboard shows the replica lag to consistently be about 20ms. However, we are seeing old results on the reader more than 90ms after a commit on the master and at least up to 170ms in some cases.</p>
  
  <p>When doing CRUD operations, our app commits the data, then issues a HTTP redirect to the client to load the new data. The network turnaround on the redirect is logged on the client and is usually at least 90ms. We are logging both the commit time and read time on the application server and see a difference of around 170ms. Old data is showing up consistently.</p>
  
  <p>Previously to Aurora we had a standard MySQL replication setup with significantly less powerful boxes and never had this issue.</p>
  
  <p>Altering the application to read and write from the same aurora instance solves the problem, but I thought Aurora used shared storage for replication. What is going on? Could this be an issue with Aurora's query cache? Is the reported replica lag inaccurate? </p>
  
  <p>Any help would be appreciated.</p>
  
  <p>Thank you,</p>