DynamoDB - Cost Optimization and Monitoring
You have a DynamoDB table with items of size 6 KB. You perform 100 eventually consistent reads per second. How many read capacity units (RCUs) do you need?
You have a DynamoDB table with items of size 6 KB. You perform 100 eventually consistent reads per second. How many read capacity units (RCUs) do you need?
medium📝 query result Q13 of 15
Step-by-Step Solution
Solution:
Step 1: Calculate RCUs per read for eventually consistent reads
One RCU allows reading 8 KB per second for eventually consistent reads, which is half the cost of strongly consistent reads.Step 2: Calculate RCUs needed for 6 KB item
6 KB item requires 2 RCUs for strongly consistent reads (since 6 KB > 4 KB, round up to 2). For eventually consistent reads, it costs half, so 1 RCU per read.Step 3: Calculate total RCUs for 100 reads
100 reads x 1 RCU = 100 RCUs.Step 4: Correct calculation
Since 6 KB is more than 4 KB, for eventually consistent reads, each read consumes ceil(6/4) = 2 RCUs * 0.5 = 1 RCU per read. So total 100 RCUs.Final Answer:
100 RCUs -> Option BQuick Check:
6 KB item eventually consistent read = 1 RCU per read [OK]
Quick Trick: Eventually consistent reads cost half RCUs [OK]
Common Mistakes:
MISTAKES- Using strongly consistent read calculation for eventually consistent
- Not rounding up item size to nearest 4 KB
- Multiplying incorrectly by number of reads
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