Question 18699 in Amazon Web Sevices Question posted in
The official Amazon Web Services documentation can be found here.

Read/Write Capacity Unit in AWS DynamoDB – Price per hour – Amazon Web Sevices

I have recently explored AWS DynamoDB and was reading about Read/Write Capacity Units. I understood that they are as under:

  • WCU: A write capacity unit represents one write per second, for
    an item up to 1 KB in size.
  • RCU: A read capacity unit represents
    one strongly consistent read per second, or two eventually consistent
    reads per second, for an item up to 4 KB in size.

So, my table has 1 WCU and 1 RCU. This means I would be charged for every read and every write I do to my table. Good so far. Plus I would be charged additionally for data storage.

However, when I look at this link (scroll down to DynamoDB detailed feature pricing/Read and Write Requests), it shows me WCU and RCU in Price per hour which is $0.00065 per WCU or $0.00013 per RCU.

What is the meaning or Price per hour?

Would I be wrong to assume $0.00065 per WCU or $0.00013 per RCU and ignore the hour part completely? Meaning, per write would cost me $0.00065 and per read would cost me $0.00013.

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Answers


  1. 0

    There are two pricing models for DynamoDB: Provisioned and On-Demand.

    Provisioned capacity means that you will be charged each hour for the provisioned unit whether you consume it or not — and your requests will be throttled if you go over provisioned capacity in a given second. This model allows for considerable savings when you have stable demand and you have a method within your solution to deal with throttles gracefully.

    If you are in the dev mode, or your application has unpredictable peaks, you should consider On-Demand mode where you will be billed a flat rate per request irrespectively of the rate of requests.

    Hope this helps.

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  2. 0

    Would I be wrong to assume $0.00065 per WCU or $0.00013 per RCU and ignore the hour part completely? Meaning, per write would cost me $0.00065 and per read would cost me $0.00013.

    Yes, for this configuration you would be charged as follows:

    Writes

    $0.00065 * 730 = $0.4745 per month

    Reads

    $0.00013 * 730 = $0.0949 per month

    In provisioned mode you pay for the capacity regardless of how many requests you make. Having 1WCU and 1RCU will allow you to write 1 * 1KB items per second and read 1 * 4KB per second. Moreover, DynamoDB free tier allows you 25WCU and 25RCU per region per month. You can apply this capacity to a single table or multiple tables as you wish. This is enough capacity to provide 200M requests per month.

    In contrast, On-demand mode allows you to pay per request, however it’s not as cost effective as provisioned mode. It simplifies using DynamoDB without needing to think about setting capacity or auto-scaling. It does not have a free tier.

    DynamoDB free tier also provides 25GB of storage per month per region.

    Have a look over the Docs… it’s filled with valuable information to help you understand the difference in capacity modes.

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