Design Facebook's Live Comments - Part 2 Take 2 (System Design Practice)

Learnings Dynamo DB internally decides the number of shards based on PK according to both the storage size and the throughput. Storage Size: Up to 10 GB per physical partition (internal shard). When this limit is exceeded, the partition is automatically split. Throughput: Each partition has a maximum capacity limit (3,000 RCU / 1,000 WCU). If traffic or provisioned/on-demand capacity requires it, the number of partitions will scale accordingly. Relation to PK (Partition Key): DynamoDB uses the hash value of the PK to determine which internal partition stores the data. So, ultimately saying, the total data size under a single partition key (PK) must not exceed 10 GB. the throughput (RCU/WCU) load must stay within the limits of a single partition.