ClickHouse

Solution

ORDER BY (the sorting key). There is no B-tree on every column. A wrong ORDER BY is a full scan. Say that before you talk about clusters.

Solution

Each insert makes parts. Too many parts and merges cannot keep up. Batch in the client or a buffer table. One-row inserts are how the cluster dies.

Solution

ClickHouse when ingest + scan latency is the product. Snowflake when governance, sharing, and SQL analysts are the product. Many companies run both.

Solution

Mutations are expensive background rewrites. Design append-only or use ReplacingMergeTree with a version. Frequent point updates belong in OLTP.

Solution

No. Keep Postgres (or similar) for transactions. ClickHouse is the analytic replica. Treating it as OLTP is the wrong interview answer.