DynamoDB and the maths around the RCUs

The question is:


Your application needs to perform 100 eventually consistent reads per second from DynamoDB. Each read is 7KB is size. What is the minimum number of RCUs required to meet this demand?


Can someone help me to understand why the answer here is 100?

Thanks!!
  • post-author-pic
    Tia W
    11-30-2018

    The way I learned to calculate eventually consistent reads is like this. :

    1.  Round  up to the nearest multiple of 4KB so in your example that would be 8KB

    2.  Divide that by 4 to get read units so that would be 8 divided by 4 = 2

    3) Multiply read units times number of items per second so that would be 100*2=200

    4) Finally, divide the last number by 2 if using eventual consistency and that would be 200 divided by 2 = 100

    Hope that helps.

  • post-author-pic
    Wagner B
    11-30-2018

    Thanks, Tia. I'll be playing with that!! :D

  • post-author-pic
    Tia W
    11-30-2018

    Make sure you pay attention to if the question is asking for seconds or minutes.  at the end you will just need to multiply at the end based on the number of seconds i.e. *60 seconds for one minute or * 120 for two minutes etc.


    We have a blog post that might be helpful as well: 

    https://linuxacademy.com/cp/socialize/index/type/community_post/id/20310

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