Design queries around round trips

Count round trips before writing SQL. Small tables can still produce slow runs when each row needs several database calls.

round trips per call × calls per run × RTT = wall time

RTT means round-trip time. This arithmetic estimates serial network time; query execution, decoding, and connection acquisition add costs.

Consider an illustrative scan of about 9k threads:

• Per-thread reads: 5 round trips × about 9.3k threads × 81 ms ≈ 63 minutes.
• Paged and batched reads: 2 round trips × 93 pages × about 100 ms ≈ 20 seconds.
• These are planning inputs. Measure RTT where the caller runs before choosing its budget.

A capability call has a constant round-trip budget, independent of result size. State that number and bound its result. A scan costs O(pages), never O(rows). Count transaction control statements and any final empty-page probe too.

Done means the store implementation matches a written query plan, and checks detect violations of its statement and access-path budgets.