Episode 4. Aurora DSQL and Limitless Database. Day 4. The deep water. This is the Principal differentiator.

Key facts. Aurora DSQL is serverless distributed SQL with virtually unlimited scale, active active multi Region writes, and strong consistency. Disaggregated storage and compute. No writer versus reader split: every node accepts writes. Say this sentence: DSQL gives you multi Region active active writes with strong consistency, which means conflicting writes are resolved by the commit protocol, not by last writer wins.

Limitless Database is the other scaling path: Aurora PostgreSQL with a sharded transaction router layer for massive write throughput on one Region. Say: Limitless scales writes horizontally inside one Region, DSQL scales writes across Regions.

Scenario 1. We moved to DSQL and now see higher commit latency on some transactions. Throughput is fine. Help.

Understand. Ask: single Region or multi Region? Which transactions slowed: single row or multi row? Cross partition or single partition? What does p50 versus p99 look like? Any hot keys?

Prepare. Say the data in order. Transaction shape and key distribution. Commit latency by percentile. Hot partition or hot key signals. Clock skew and cross Region round trip contribution. Retry and conflict rates.

Say your translation line: Same instinct as RAC interconnect and global cache waits: the commit path now crosses a network.

Identify. Rank the hypotheses. One: multi partition transactions paying two phase commit cost. Two: hot keys causing contention and retries. Three: cross Region round trips on the commit path. Four: wrong partition key forcing scatter gather. Fix: keep transactions single partition where possible, redesign hot keys, choose partition keys that colocate the working set.

Support. Success: p99 commit latency back to target, conflict and retry rates flat, and an alarm on hot partition share.

Scenario 2: choosing between Aurora provisioned, Limitless, and DSQL. Say: I'd choose provisioned Aurora for predictable single Region relational workloads, Limitless for extreme single Region write scale, and DSQL for multi Region active active with strong consistency needs. Then commit. Say: my recommendation is.

Isolation levels matter here. Know read committed versus repeatable read versus serializable, and what DSQL guarantees. Interviewers probe exactly this seam.

Your Day 4 lab: on paper, design a partition key for an orders workload, list three transactions that stay single partition, and rewrite one that cannot. Then read the DSQL docs on consistency and write down the guarantee in one sentence.

Tomorrow, Episode 5: DynamoDB. Hot partitions, throttling, and single table design. Understand. Prepare. Identify. Support. Say it again.