Interview room
10TB query takes 30 minutes: prune, cluster, MV, rewrite, size. Evidence before folklore.
Basics
Bytes scanned dominate. Partition pruning. Clustering. Rewrite without SELECT *. MVs for repeated grains. Size after scan health.
Prompt
Plan/bytes; layout; SQL; aggregates; sizing; keep metric meaning.
Good
Bytes first; prune; rewrite; cluster; MV; then size.
Clarify/scope
Interactive vs ELT; can add aggregates; concurrency.
Scoring lens: Optimize Query Performance in Warehouse
Interviewers reward incident-first teaching, a clear control loop, and named owners. Tool logos without that loop score poorly.
Weak vs strong answers on Optimize Query Performance in Warehouse
Weak: list products. Strong: tell the failure story, define the mechanism, draw the path, state rollout and monitors.
Scope control
Say what is out of scope for v1. Come back only if follow-ups demand it. This is a seniority signal for Optimize Query Performance in Warehouse.
Clarifying then committing
Ask a few high-use questions about SLAs, owners, and scale, then sketch. Endless questions without a diagram look evasive.
Before/after scoreboard
Record bytes scanned, partitions pruned, runtime, and warehouse size before and after each change. Optimization without numbers is storytelling.
Semantic safety
If a "rewrite" adds filters that drop late events, call it a metric change. Performance work that alters KPIs is a data incident.
Concurrency after scan health
Once queries scan 100GB not 10TB, warehouse sizing and isolation matter. Until then, XL is an expensive waiting room.
Interview framing detail 1
For lb-sd-36, spend the first minutes making the problem concrete: who gets hurt when this fails, what SLA is implied, and what is explicitly out of scope. Then teach the prerequisite concept before proposing boxes. A candidate who names vendors first usually loses the plot. Write two clarifying questions on the board and answer them with assumptions if the interviewer shrugs. Keep the first diagram small enough to redraw when a follow-up changes a constraint.
Interview framing detail 2
For lb-sd-36, spend the first minutes making the problem concrete: who gets hurt when this fails, what SLA is implied, and what is explicitly out of scope. Then teach the prerequisite concept before proposing boxes. A candidate who names vendors first usually loses the plot. Write two clarifying questions on the board and answer them with assumptions if the interviewer shrugs. Keep the first diagram small enough to redraw when a follow-up changes a constraint.
Interview framing detail 3
For lb-sd-36, spend the first minutes making the problem concrete: who gets hurt when this fails, what SLA is implied, and what is explicitly out of scope. Then teach the prerequisite concept before proposing boxes. A candidate who names vendors first usually loses the plot. Write two clarifying questions on the board and answer them with assumptions if the interviewer shrugs. Keep the first diagram small enough to redraw when a follow-up changes a constraint.
Interview framing detail 4
For lb-sd-36, spend the first minutes making the problem concrete: who gets hurt when this fails, what SLA is implied, and what is explicitly out of scope. Then teach the prerequisite concept before proposing boxes. A candidate who names vendors first usually loses the plot. Write two clarifying questions on the board and answer them with assumptions if the interviewer shrugs. Keep the first diagram small enough to redraw when a follow-up changes a constraint.
Interview framing detail 5
For lb-sd-36, spend the first minutes making the problem concrete: who gets hurt when this fails, what SLA is implied, and what is explicitly out of scope. Then teach the prerequisite concept before proposing boxes. A candidate who names vendors first usually loses the plot. Write two clarifying questions on the board and answer them with assumptions if the interviewer shrugs. Keep the first diagram small enough to redraw when a follow-up changes a constraint.
Interview framing detail 6
For lb-sd-36, spend the first minutes making the problem concrete: who gets hurt when this fails, what SLA is implied, and what is explicitly out of scope. Then teach the prerequisite concept before proposing boxes. A candidate who names vendors first usually loses the plot. Write two clarifying questions on the board and answer them with assumptions if the interviewer shrugs. Keep the first diagram small enough to redraw when a follow-up changes a constraint.