Capacity Units

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As was discussed earlier in the “Salient Features of DynamoDB” lesson we are charged for the frequency of our reads and writes, instead of for the storage we use. We can choose one of the two following options for running our table:

  1. On-demand provisioning: In this provisioning, AWS will scale our provision capacity up or down based on our usage. We do not have to define our throughput units.
  2. Provisioned capacity: In this option, we specify upfront how much capacity, based on our estimated reads and writes per second, we will use.

We will discuss the calculation behind the capacity unit next.

Write capacity

One write capacity unit means DynamoDB will support one write per second for an item sized at 1KB. If the item size is greater than 1KB, say 10KB, it will need more capacity units, i.e. in this case, it will need 10 capacity units. For strong consistency in writes, we will need two write capacity units to write an item sized at 1 KB in one second.

Let’s look at a calculator to understand this better.

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