dynamodb-table

aws.dynamodb.table

Fully-managed key-value store; single-digit-ms reads/writes at any scale. Config knobs here: billingMode, pointInTimeRecovery, streamEnabled. When to pick DynamoDB at all → data-modeling.md; key/index design rules → db-indexing.md.

Hard limits (apply regardless of billingMode — scaling capacity does NOT fix a hot key)

• Per partition: 3,000 RCU / 1,000 WCU = 12MB/s reads (3,000 × 4KB), 1MB/s writes (1,000 × 1KB), ~10GB data (partitions auto-split on size/throughput). A single hot partition key caps at these numbers; mitigation patterns → sharding.md.
• 400KB max item size (all attributes). Bigger payloads: store blob in S3, keep a pointer + metadata in the item.
• Writes round up to 1KB min (a 50-byte counter write still costs 1 WCU); reads round up to 4KB.

billingMode

• PAY_PER_REQUEST (default, on-demand): per-request pricing, ~$1.12/M reads (4KB) and ~$5.62/M writes (1KB). Right for spiky/unpredictable or low traffic — no capacity planning.
• Switch to PROVISIONED for steady, predictable high traffic: ~$0.00065/WCU-hour, materially cheaper at sustained load (on-demand is "significantly higher" at scale — e.g. 10M writes/s ≈ $156K/day even provisioned). Rule of thumb: sustained utilization → provisioned + auto-scaling; otherwise keep the default.

Reads & consistency

• Consistency is per-request, not table config: ConsistentRead=true on GetItem/Query/Scan. Strong reads cost 2x (1 RCU/4KB vs 0.5) and only work on base table + LSIs — never on GSIs.
• Avoid Scan; Query on keys only. ProjectionExpression trims bandwidth but you still pay full RCU for item size — split large cold attributes into a separate table/item.

GSIs (mechanics only — when/how to design keys → db-indexing.md)

• A GSI is effectively a separate table: own partitions, own capacity (under provisioned mode, provision it separately), updated asynchronously → eventually consistent only, with replication lag.
• Write amplification: every base-table write fans out to each affected GSI. Max 20 GSIs; LSIs (max 5, same-partition, support strong reads, 10GB/partition-key cap) must be defined at table creation.