How can I check the item size of a request in dynamodb?

Question

We are using a dynamodb with on-demand capacity mode. We are suddenly seeing few of our requests getting write throttled. During the same time frame there is sudden spike in Write Capacity Units (WCU).

I have checked the incoming traffic/ write request count and it is pretty much the same.

1. Does this mean the WCU increase is due to increase in item size?
2. How can I verify the size of my request?
3. Since our dynamodb is already provisioned in on-demand mode, why is it unable to auto scale and handle the requests given that traffic is pretty much the same.

Answer 1

1. It's possible

2. You can return the consumed capacity for each write operation which will allow you to understand which items are consuming more capacity. ReturnConsumedCapacity

3. On-demand mode tables can throttle for 3 reasons:

   • You exceed twice your previous peak in 30 mins
   • You exceed partition hard limit of 1000 WCU / 3000 RCU (hot partition)
   • You have GSI backoressure where you're GSI has a hot partition

You can enable CloudWatch Contributor Insights to understand if you have a hot key(s).