Root Cause Analysis for Systems

Root cause analysis (RCA) is a systematic investigation technique used to identify the fundamental underlying cause(s) of a system failure, rather than just addressing the immediate symptoms. In AI/ML systems, RCA is essential because failures often have complex, multi-layered causes.

RCA Methods

• Five Whys: Repeatedly ask "why?" to drill deeper into the cause chain. Example: "The model returned nonsense" → Why? "The prompt was malformed" → Why? "The template variable was null" → Why? "The user session expired" → Why? "The session timeout was too short for long-running queries."
• Fishbone Diagram (Ishikawa): Categorize potential causes into groups — People, Process, Technology, Data, Environment — and systematically analyze each branch.
• Fault Tree Analysis: Build a tree of events that could lead to the failure, with AND/OR gates showing how causes combine.
• Timeline Analysis: Reconstruct the exact sequence of events leading to the failure to identify the triggering change or condition.

Common Root Causes in AI Systems

• Data Quality: Training data issues (contamination, bias, distribution shift) that cascade into model behavior problems.
• Configuration Changes: Updated system prompts, modified parameters, rotated API keys that inadvertently break functionality.
• Deployment Issues: Incomplete rollouts, version mismatches, missing dependencies, incompatible model-tokenizer pairs.
• Capacity: Insufficient GPU memory, exceeded rate limits, queue overflow under unexpected load.
• External Dependencies: Third-party API changes, provider outages, upstream data source modifications.

RCA Best Practices

• Look for Systemic Issues: Individual errors are symptoms — the root cause is usually a process or system gap that allowed the error to have impact.
• Multiple Root Causes: Complex incidents often have multiple contributing factors — don't stop at the first cause you find.
• Actionable Outcomes: Every root cause should map to a specific preventive action — if you can't act on it, dig deeper.
• Avoiding Blame: Focus on "what" and "how," not "who" — punishing individuals discourages honest reporting.

Root cause analysis transforms every failure into an improvement opportunity — without it, organizations keep fighting the same fires repeatedly.