Two examples of tools that I could not use because my clients had their database on Heroku were PGRepack (reducing extended bloat without database downtime) and AWS Database Migration Service (seamless replication between database types). You’ll probably not be aware that your app needs these tools before it’s too late. It means that a whole variety of tools and techniques won’t work on the Heroku addon. Limited permissionsĪnother potential issue of running your application on Heroku PostgreSQL is the fact that it does not grant superuser permissions. Still, if your Heroku database cannot achieve a decent cache hit ratio and memory usage is consistently high, then a switch to RDS could be a viable solution. Maybe it was a one-time edge case scenario. AWS RDS allows tweaking all the PostgreSQL settings, potentially letting you squeeze out better performance from the same hardware configuration. Heroku premium-2 plan has a hardcoded value of 64MB, meaning that each client connection can consume more memory leaving less for caching. For example, for a database with 8GB of RAM, PGTune tool recommends setting work_mem to 5MB. One possible explanation for this phenomenon is the high (and hardcoded) value for work_mem PostgreSQL setting on Heroku. You have to look for the following entries: sample#memory-total =62560050kB sample#memory-free =11327524kBĪfter moving to AWS RDS, memory usage dropped by ~30%, and cache hits were finally consistently over 99%. You should see the PostgreSQL plugin logs output. On Heroku, you can check the current memory usage by running: heroku logs -t | grep heroku-postgres Despite the lack of heavyweight queries, the RAM usage instantly spiked to over 99% after the warm-up, but the cache hit ratio did not improve.īTW please don’t confuse memory usage with cache hit ratio! High cache hit ratio - GOOD, high RAM memory usage - BAD. Even upgrading the Heroku database plan did not increase it. I don’t have more proof than an anecdoate evidence but one of my clients had an issue with cache hit ratio consistently below 90%. A lower ratio means that the database is under-scaled or misconfigured, significantly slowing down the performance. You can check this value for your Heroku database by installing heroku-pg-extras plugin and running: heroku pg:cache-hitĮfficiently tuned databases should read over 99% of data from memory. RDSĬache hit ratio is a critical metric that indicates how much data is read from the in-memory cache instead of a slow hard drive.
Memory usage and cache hit ratio Heroku vs. Because underlying hardware and network are the same, there’s no performance impact of using the RDS with the Heroku application dynos. Europe is located in the AWS Ireland region ( eu-west-1), United States in AWS North Virginia ( us-east-1). They currently offer two regions for public spaces: the United States and Europe. The reason is that Heroku uses AWS as an infrastructure provider. We’ve never noticed a measurable networking layer overhead after the switch. I’ve helped multiple projects to migrate their database from Heroku to AWS RDS as a part of my Rails performance audits. Is there a performance overhead of using the RDS database on Heroku? Private spaces are an enterprise feature, and the pricing starts from $1000/month. I write this blog post in the context of the default Heroku public spaces. I’ll also compare the pricing, available features, performance characteristics and explain why projects that care about EU GDRP compliance should avoid using the Heroku database. In this blog post, I’ll describe the benefits and drawbacks of using AWS RDS instead of the default Heroku addon. Once your web app matures, then migrating to an alternative database engine like Amazon RDS should be considered.
Heroku PostgreSQL addon is excellent for a quick start setup of a new project. A leading-edge performance and error monitoring tool for Ruby applications.
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