Phase 4.0 Cache Checkpoint - Summary
Status
Phase 4.0 checkpoint: ✅ Complete
Decision: No runtime cache change proposed
Comprehensive validation: ❌ Not complete
Core Decision
No per-style Cell cache capacity or eviction change is justified by the currently measured synthetic workloads.
Keep unchanged:
- MAX_CACHED_CELLS_PER_STYLE = 128
- Clear-all eviction policy
- No LRU/LFU implementation
Rationale: Insufficient evidence to justify modification, not proof of optimality.
What Was Measured
- 8 synthetic profiler workloads
- Cell cache hit rates and bucket distribution
- Text cache behavior (limited coverage)
- Wrap cache width-bucket behavior
- Grapheme timing (advisory, single-run)
Key Findings
Per-Style Cell Capacity
- Decision: No change justified
- Data: Repeated CJK 99.98% hit, Mixed 37.49% hit, 0 clears
- Limitation: Mixed uses fresh Style per line (sharded), doesn't validate reused styles
Eviction Strategy
- Decision: Inconclusive
- Limitation: No post-clear reuse workload
Text Cache Sizing
- Decision: Inconclusive
- Limitation: 1000 < MAX 1024, capacity not exercised
Wrap Cache
- Decision: Per-width capacity not measured
- Data: Outer width-bucket instrumentation validated
Grapheme
- Decision: Not measured with decision-grade timing
- Conclusion: Inconclusive (counter coverage confirmed; no isolated segmentation benchmark)
Long Text / inlineLineCache
- Decision: Not measured
Style Cardinality
- Decision: Not measured (registered ≠ live)
Critical Limitations
Measurement Issues
- Heap measurements invalid for retained-memory analysis (excluded from decisions)
- Registered buckets ≠ live production buckets
- Mixed workload artificially sharded (fresh Style per line)
Coverage Gaps
- No reused style with >128 characters
- No eviction-sensitive workload
- No capacity threshold testing
- No long text scenarios
- No production traces
What Is NOT Claimed
❌ Current cache is validated ❌ Current cache performs well (globally) ❌ 90%+ safety margin for reused styles ❌ Segmentation is cheap ❌ Text/wrap sizing is adequate ❌ All gates failed ❌ Cache work complete
Next Steps
Required: Phase 3 Disabled-Path Overhead Validation
This is mandatory and independent of cache-tuning decisions.
Phase 3 instrumentation hooks are in production hot paths (createCell, textCellWidth, wrapByCells). The disabled-path production overhead must be validated.
Compare:
- Pre-Phase-3 commit (before PR #116)
- Current main with instrumentation disabled
Requirements:
- Isolated processes or separate worktrees
- Randomized/alternating execution order
- Warmup + multiple samples
- p50/p95 comparison with confidence intervals
- Use Phase 2 baseline harness
Tracked in #119.
Optional: Phase 4.1 Cache Workload Validation
Phase 4.1 is optional only if cache optimization is explicitly deferred.
Required before:
- Claiming cache strategy is validated
- Changing cache capacity or eviction
- Closing cache evaluation as complete
If pursued, add:
- Stable style + high diversity + multiple passes
- Eviction-sensitive patterns
- Capacity threshold tests
- Long text scenarios
- Production traces
Conclusion
Phase 4.0 is a checkpoint, not comprehensive validation.
Engineering decision: Keep implementation unchanged due to insufficient evidence for change.
Not a validation that current cache is optimal or adequate for all scenarios.