In Amazon DynamoDB, read and write capacity units (RCUs and WCUs) are measures used to provision and manage the throughput capacity of a DynamoDB table. Throughput capacity determines the maximum number of read and write operations that a table can handle per second. Here's a detailed explanation of RCUs and WCUs:
Read Capacity Units (RCUs) :
* Read capacity units (RCUs) represent the throughput capacity for read operations in a DynamoDB table.
* One read capacity unit (RCU) represents one strongly consistent read per second for items up to 4 KB in size, or two eventually consistent reads per second for items up to 4 KB in size.
* When performing read operations, DynamoDB consumes RCUs based on the consistency level specified for the read operation (strongly consistent or eventually consistent).
* For larger item sizes, DynamoDB consumes additional RCUs. For example, a read operation on an item of 8 KB consumes two RCUs for strongly consistent reads or four RCUs for eventually consistent reads.
Write Capacity Units (WCUs) :
* Write capacity units (WCUs) represent the throughput capacity for write operations in a DynamoDB table.
* One write capacity unit (WCU) represents one write operation per second for items up to 1 KB in size.
* Write operations include inserts, updates, and deletes.
* For larger item sizes, DynamoDB consumes additional WCUs. For example, a write operation on an item of 2 KB consumes two WCUs.
Provisioned Throughput :
* DynamoDB uses provisioned throughput to manage and allocate RCUs and WCUs for a table.
* Users can provision read and write capacity for their tables based on anticipated workload requirements.
* Throughput capacity is allocated in units of RCUs and WCUs, with users specifying the desired number of units when creating or updating a table.
Scaling and Auto Scaling :
* DynamoDB allows users to manually adjust provisioned throughput capacity as needed, either increasing or decreasing RCUs and WCUs based on changing workload requirements.
* Additionally, DynamoDB offers auto scaling, a feature that automatically adjusts throughput capacity in response to changes in traffic patterns.
* With auto scaling enabled, DynamoDB dynamically adjusts the number of provisioned RCUs and WCUs based on actual usage, ensuring that applications can handle varying levels of traffic without being over-* provisioned or under-provisioned.
Cost Considerations :
* DynamoDB pricing is based on provisioned throughput capacity (RCUs and WCUs), with users paying for the provisioned capacity regardless of actual usage.
* It's important for users to carefully estimate their throughput capacity requirements to avoid over-provisioning and unnecessary costs.
* Users can monitor throughput usage and adjust provisioned capacity as needed to optimize costs while ensuring adequate performance.
