worldmonitor/todos/158-complete-p2-scenario-heat-layer-set-alloc-every-build.md

status, priority, issue_id, tags, dependencies

status	priority	issue_id	tags	dependencies
complete	p2	158	code-review performance supply-chain deckgl

createScenarioHeatLayer Allocates New Set on Every buildLayers() Call

Problem Statement

DeckGLMap.createScenarioHeatLayer() constructs new Set(this.scenarioState.affectedIso2s) inside the method body. buildLayers() is called on every frame/render cycle by DeckGL when layers need to be rebuilt. The Set allocation is O(n) on the number of affected ISO-2 codes and runs inside the hot DeckGL render path.

Findings

• File: src/components/DeckGLMap.ts
• Code:

  private createScenarioHeatLayer(): GeoJsonLayer | null {
    if (!this.scenarioState?.affectedIso2s?.length || !this.countriesGeoJsonData) return null;
    const affected = new Set(this.scenarioState.affectedIso2s);  // ← allocated every call
    return new GeoJsonLayer({ ..., getFillColor: (feature) => { const code = ...; return affected.has(code) ? ... } });
  }
  

• buildLayers() is called whenever deck viewport or layers change — potentially dozens of times per second during pan/zoom
• The Set contents only change when setScenarioState() is called (rare)
• Identified by performance-oracle during PR #2910 review

Proposed Solutions

Option A: Cache the Set in setScenarioState() (Recommended)

private affectedIso2Set: Set<string> = new Set();

public setScenarioState(state: ScenarioVisualState | null): void {
  this.scenarioState = state;
  this.affectedIso2Set = new Set(state?.affectedIso2s ?? []);
  this.rebuildLayers();
}

private createScenarioHeatLayer(): GeoJsonLayer | null {
  if (!this.affectedIso2Set.size || !this.countriesGeoJsonData) return null;
  return new GeoJsonLayer({ ..., getFillColor: (feature) => {
    const code = feature.properties?.['ISO3166-1-Alpha-2'] as string | undefined;
    return (code && this.affectedIso2Set.has(code) ? [220, 60, 40, 80] : [0, 0, 0, 0]) as [number,number,number,number];
  }});
}

Pros: Set allocated once per state change (not per render), correct updateTriggers still invalidates DeckGL cache Cons: Small memory overhead for the cached Set field Effort: Small | Risk: Low

Option B: Keep as-is with a comment

Acceptable if buildLayers() is only called on state change. But DeckGL calls it more often. Effort: None | Risk: High (performance regression on active globe interactions)

Recommended Action

Apply Option A — cache the Set in setScenarioState().

Technical Details

• Affected files: src/components/DeckGLMap.ts
• Add private affectedIso2Set: Set<string> = new Set() field
• Move Set construction to setScenarioState()

Acceptance Criteria

• createScenarioHeatLayer does not allocate a new Set on each call
• setScenarioState() rebuilds the cached Set
• npm run typecheck passes

Work Log

• 2026-04-10: Identified by performance-oracle during PR #2910 review

Resources

• PR: #2910