PERFORMANCE OBSERVABILITY — PHASE 3¶

Status¶

• Phase: 3
• Authority: Normative
• Scope: Measurement-only, non-influential
• Dependencies:
• PERF_VISION.md
• PERF_INVARIANTS.md
• PERF_PROOF_RULES.md
• PERFORMANCE_BASELINE.md
• CRITICAL_PATHS.md
• SEMANTIC_EQUIVALENCE.md

This document defines the only allowed observability mechanisms for performance analysis in Phase 3.

If observability influences behavior, correctness, ordering, or timing, it violates Phase 3 invariants and is forbidden.

1. Purpose¶

Phase 3 requires insight into performance without changing semantics.

This document defines: - What performance data may be collected - Where instrumentation may exist - What instrumentation MUST NOT do - How determinism is preserved

Observability exists to observe, never to decide.

2. Observability Principle¶

OBSERVABILITY PRINCIPLE (Binding)¶

Observability MUST be strictly passive.

This means: - Observability may record - Observability may count - Observability may timestamp - Observability may expose metrics

It may never: - Influence control flow - Influence scheduling - Influence batching - Influence retry logic - Influence resource usage decisions

If removing observability changes behavior, observability is incorrect.

3. Permitted Observability Outputs¶

The following outputs are permitted:

3.1 Metrics¶

• Counters
• Gauges
• Histograms
• Deterministic timers

Metrics MUST: - Be monotonic where applicable - Have explicit units - Be emitted in deterministic order

3.2 Logs¶

• Structured logs
• Event logs
• Lifecycle logs

Logs MUST: - Be append-only - Never gate behavior - Never suppress errors

3.3 Traces (Internal Only)¶

• Internal execution spans
• Phase boundaries
• Critical path markers

Traces MUST: - Be disabled by default - Not alter execution shape - Not allocate unbounded memory

4. Forbidden Observability Patterns¶

The following patterns are explicitly forbidden:

• Metric-driven branching
• Threshold-based behavior changes
• Adaptive batching using metrics
• Backpressure driven by observability
• Sampling that affects execution
• Best-effort metric emission
• Dropping metrics silently
• Async observability affecting ordering

Observability MUST NOT introduce feedback loops.

5. Determinism Requirements¶

5.1 Deterministic Emission¶

Observability output MUST be:

• Deterministically ordered
• Independent of scheduling
• Independent of timing variance

For identical executions: - Metric sequences MUST be identical - Log sequences MUST be identical (excluding timestamps if explicitly allowed)

5.2 Timestamp Rules¶

Timestamps: - MAY be recorded - MUST NOT be interpreted - MUST NOT affect control flow

Timestamps are diagnostic only.

6. Placement Rules¶

6.1 Critical Path Instrumentation¶

Instrumentation MAY exist on critical paths ONLY if:

• It does not allocate unbounded memory
• It does not block
• It does not perform I/O
• It does not acquire new locks

If instrumentation adds blocking or contention, it is invalid.

6.2 Non-Critical Paths¶

Heavier instrumentation MAY exist on non-critical paths ONLY if:

• It is explicitly documented
• It is disableable
• It does not influence critical paths

7. Error Handling in Observability¶

• Observability failures MUST NOT affect execution
• Metrics emission failures MUST be ignored safely
• Logging failures MUST NOT suppress errors

If observability fails, the system continues unmodified.

8. Interaction with Optimizations¶

Optimizations MUST NOT:

• Read observability outputs
• Infer state from metrics
• Use observability to tune behavior
• Depend on observability being enabled

Observability MUST remain orthogonal to optimization logic.

9. Configuration Rules¶

9.1 Enablement¶

• Observability may be enabled or disabled at startup
• Enablement MUST NOT change behavior
• Enablement MUST NOT affect recovery

9.2 Runtime Changes¶

Runtime observability toggling is allowed ONLY if:

• It does not alter code paths
• It does not alter allocation patterns
• It does not alter execution order

If toggling changes execution shape, it is forbidden.

10. Observability and Failure Model¶

Observability MUST be correct under failures:

• Crash during metric emission
• Crash during logging
• Partial observability output

Failure outcomes: - MUST NOT corrupt WAL - MUST NOT corrupt snapshots - MUST NOT affect recovery

Observability state is non-authoritative and discardable.

11. Testing Requirements¶

Observability MUST be tested to prove:

• Removal does not change behavior
• Enablement does not change behavior
• Failures in observability do not affect execution

Tests MUST: - Compare observable DB behavior with and without observability - Pass all Phase 1 and Phase 2 regressions unmodified

12. Explicit Non-Goals¶

Performance observability does NOT aim to:

• Auto-tune AeroDB
• Adapt execution strategies
• Replace profiling tools
• Predict performance

It exists only to measure what already happens.

13. Proof Obligations¶

Any Phase 3 optimization that adds observability MUST:

• Reference this document
• Prove passivity
• Prove determinism
• Prove disablement safety

If proof is omitted, optimization is invalid.

14. Final Rule¶

Observability that influences behavior
is no longer observability — it is control logic.

Phase 3 permits measurement only. All decision-making remains explicit and semantic.

END OF DOCUMENT