AWS Brief 10-Point Guides Databases

A Brief 10-Point Guide to AWS DynamoDB

When I’m learning new about new technologies, one of the first things, I’ll do is write a numbered list 1-10 and then fill that numbered list in with points about that particular technology. I realised that these lists might be useful to others so I’m going to start posting them. This week I looked at AWS DynamoDB.

  1. Amazon’s DynamoDB is fully managed key-value and document database
  2. As DynamoDB is fully managed, one of the benefits of using it is that there is no server to manage and more importantly DynamoDB auto-scales to the demand on the database as a result the performance of the AWS DynamoDB is consistent at scale.
  3. Performance is another reason to use DynamoDB. Amazon boasts: ‘single-digit millisecond response times at any scale’
  4. Data safety is another benefit of using DynamoDB. Amazon enables instant backups of ‘hundreds of terabytes of data’ with no performance impact. Further, with DynamoDB it is possible to restore the database to any state that existed within the last 35 days. More impressive is that this can be done with no downtime.
  5. A seldom mentioned, but very important benefit of using DynamoDB is that Amazon provides the ability to deploy instances of DynamoDB locally, which is very useful for testing your application. Being able to deploy a local instance of DynamoDB means that you can run your integration tests against that instance, which provides a more valid test context, which means you are more likely to catch bugs that would occur in production therefore enabling you to improve the quality of your code and speed up the development cycle.
  6. Another benefit of using DynamoDB is that it accommodates cases where some data is accessed more than other data while still providing autoscaling. To understand this benefit, it is important to understand that this wasn’t always the case. It used to be the case that with autoscaling just sticking the data in DynamoDB could lead to a problem where performance would be impacted or queries would error. The reason for this is that DynamoDB when autoscaling would shard the data with the assumption that all the data will be accessed with uniform frequency. It did not consider what data is most important. Not all data is created equal. Some data will be accessed far more often than other data. The term for this is a ‘hot key’. In other words, it used to assume that you will access each key in the database roughly an equal number of times, which often isn’t the case. However, now DynamoDB has a feature called adaptive capacity, which, as of 2019, will instantly adapt to your data. In other words the sharding process which occurs during autoscaling distributes your data according to the demands on different keys. This is remarkable. What’s more, this is done at no additional cost and it does not have to be configured.
  7. Perhaps one of the drawbacks of using DynamoDB is that the costs of using it can balloon if you experience spikes in demand or if you haven’t done a good job of predicting what the demand on your database will be. While Amazon does provide a pricing calculator to help you estimate your costs, it is still dependent on your assumptions and estimates. This drawback is really tradeoff for the autoscaling capacity that DynamoDB provides. One of the things you should therefore ask your self is are you expecting fluctuations in demand that would benefit from DynamoDB’s autoscaling?
  8. Another drawback of using DynamoDB is that it has a limit on individual binary items of 400kb. This means that DynamoDB is not well-suited to storing images or large documents.
  9. In DynamoDB, scanning a table is not an efficient operation, which can of course be problem depending on the structure of your data and your use case. In furtherance, this may lead to to incur addition costs over what was initially planned, scanning the whole table in DynamoDB is expensive. This may lead you desire additional indexes, particularly secondary global indexes, which can be provisioned at an additional cost particularly because of the additional cost in writing to DynamoDB.
  10. A final drawback to consider is that write operations to DynamoDB are expensive. Writes to DynamoDB are prices via ‘Write Capacity Units’ per month. When you have a use case with a lot of writes this cost can balloon.

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