Provisioned WCU Calculation for DynamoDB Table

Answer: B.

Option B is CORRECT.

One write capacity unit is equivalent to one write per second for an item up to 1 KB in size.

Thus, the required WCU in this scenario is 6KB x 40 write operations per second = 240 WCU.

Reference:

To determine the provisioned WCU value required to meet the read and write requirements of the application, we need to consider the following:

• Read Capacity Units (RCUs): One RCU can read one item of size up to 4 KB per second in eventual consistency mode. For strongly consistent reads, one RCU can read one item of size up to 4 KB per second. For items larger than 4 KB, additional RCUs are required for each 4 KB of data.
• Write Capacity Units (WCUs): One WCU can write one item of size up to 1 KB per second. For items larger than 1 KB, additional WCUs are required for each additional KB of data.

Given that each item in the table is 6 KB in size, we need to calculate the number of RCUs and WCUs required to meet the application's needs:

• For the 100 eventually consistent read operations per second, we need 100 RCUs. Since each item is 6 KB in size, we need to divide the item size by 4 KB (the size that one RCU can read in eventual consistency mode) and round up to the nearest integer: 6 KB / 4 KB = 1.5, rounded up to 2 RCUs per item. Therefore, the total RCUs required are: 100 * 2 = 200 RCUs.
• For the 40 write operations per second, we need 40 WCUs. Since each item is 6 KB in size, we need to divide the item size by 1 KB (the size that one WCU can write) and round up to the nearest integer: 6 KB / 1 KB = 6 WCUs per item. Therefore, the total WCUs required are: 40 * 6 = 240 WCUs.

Therefore, the provisioned WCU value required to meet these requirements is 240 WCUs, which corresponds to answer B.