The original title is "Day 60: ClickHouse® Query Profiling – Finding Performance Bottlenecks"

Short summary

ClickHouse provides built-in profiling tools—system.query_log, EXPLAIN, and ProfileEvents—that expose why queries are slow: excessive data scanning, expensive calculations, memory pressure, or network overhead. Identify the actual bottleneck (I/O, CPU, memory, or network) before optimizing; blindly adding hardware wastes resources. Follow a systematic workflow: find slow queries, inspect execution plans, review metrics, apply targeted fixes, then measure results.

• •Use system.query_log and ProfileEvents to identify actual bottlenecks rather than guessing based on symptoms
• •Profile systematically: EXPLAIN, review metrics, apply targeted optimizations, measure results
• •Common bottlenecks: inefficient filtering/primary keys, large aggregations/joins, memory pressure, disk I/O, network overhead

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