title: Low Postgres Cache Hit Ratio - data size or something else?
body: <p>I've just upgraded my Heroku postgres database from the Kappa plan (800MB RAM, postgres 9.1) to the Ronin plan (1.7GB RAM, postgres 9.2), but performance has degraded.</p>
  
  <p>Following the guide <a href="https://devcenter.heroku.com/articles/heroku-postgres-plans#cache-size">here</a>, I checked and the cache hit rate is even lower than it was with our Kappa database (now ~57%, previously ~69%). Our app design should be decently ok, as we've seen a cache hit rate of ~99% before.</p>
  
  <p>The recommendation is that the data set should be able to fit into memory, which shouldn't be a problem now - our data size is 1.27GB (at least most of it should fit).</p>
  
  <p>Is the low cache hit rate due to the data size, or is there something else I can look into? Or is it simply a case of the database cache not fully warmed up? (it's been almost 2 days)</p>