fix: correct cache eviction formula to prioritize high-value items
Fixed inverted eviction scoring formula in UnifiedCache that was causing metadata (cheap to rebuild) to be retained while HNSW vectors (expensive, frequently accessed) were evicted. This was causing OOM crashes during large Excel imports with relationship extraction. Changes: - evictLowestValue(): Changed accessScore / rebuildCost to accessScore * rebuildCost - evictForSize(): Changed accessScore / rebuildCost to accessScore * rebuildCost - evictType(): Changed accessScore / rebuildCost to accessScore * rebuildCost With the corrected formula, items with higher access counts AND higher rebuild costs get higher scores and are protected from eviction. Test coverage: Added comprehensive eviction scoring tests Fixes: Type metadata hogging 99.7% of cache with only 3.7% access rate
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2 changed files with 238 additions and 6 deletions
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@ -241,9 +241,9 @@ export class UnifiedCache {
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let lowestScore = Infinity
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for (const [key, item] of this.cache) {
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// Calculate value score: access frequency / rebuild cost
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// Calculate value score: access frequency * rebuild cost (higher is better)
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const accessScore = (this.access.get(key) || 1)
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const score = accessScore / Math.max(item.rebuildCost, 1)
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const score = accessScore * item.rebuildCost
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if (score < lowestScore) {
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lowestScore = score
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@ -267,9 +267,9 @@ export class UnifiedCache {
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*/
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evictForSize(bytesNeeded: number): boolean {
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const candidates: Array<[string, number, CacheItem]> = []
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for (const [key, item] of this.cache) {
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const score = (this.access.get(key) || 1) / item.rebuildCost
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const score = (this.access.get(key) || 1) * item.rebuildCost
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candidates.push([key, score, item])
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}
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@ -349,10 +349,10 @@ export class UnifiedCache {
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*/
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private evictType(type: 'hnsw' | 'metadata' | 'embedding' | 'other'): void {
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const candidates: Array<[string, number, CacheItem]> = []
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for (const [key, item] of this.cache) {
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if (item.type === type) {
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const score = (this.access.get(key) || 1) / item.rebuildCost
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const score = (this.access.get(key) || 1) * item.rebuildCost
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candidates.push([key, score, item])
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}
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}
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232
tests/unit/utils/unifiedCache-eviction.test.ts
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232
tests/unit/utils/unifiedCache-eviction.test.ts
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@ -0,0 +1,232 @@
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/**
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* UnifiedCache Eviction Scoring Tests
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* Verify that cache eviction properly prioritizes items based on
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* access frequency and rebuild cost
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*/
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import { describe, it, expect, beforeEach } from 'vitest'
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import { UnifiedCache } from '../../../src/utils/unifiedCache'
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describe('UnifiedCache Eviction Scoring', () => {
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let cache: UnifiedCache
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beforeEach(() => {
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// Create cache with small size for testing
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cache = new UnifiedCache({ maxSize: 1000 })
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})
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it('should evict low-value metadata before high-value HNSW vectors', () => {
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// Add metadata entry (low rebuild cost, low access count)
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cache.set('meta1', { data: 'metadata' }, 'metadata', 100, 1)
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// Add HNSW vector (high rebuild cost, high access count)
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cache.set('hnsw1', { data: 'vector' }, 'hnsw', 100, 50)
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// Simulate frequent access to HNSW
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for (let i = 0; i < 10; i++) {
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cache.getSync('hnsw1')
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}
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// Fill cache to force eviction
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cache.set('new1', { data: 'newdata' }, 'other', 900, 1)
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// With CORRECT formula (accessCount * rebuildCost):
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// meta1 score: 1 * 1 = 1 (should be evicted)
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// hnsw1 score: 11 * 50 = 550 (should be kept)
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const stats = cache.getStats()
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// HNSW should be kept (high value)
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expect(cache.getSync('hnsw1')).toBeDefined()
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// Metadata should likely be evicted (low value)
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// Note: Since we're filling most of cache, metadata is candidate for eviction
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expect(stats.typeSizes.hnsw).toBeGreaterThan(0)
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})
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it('should prioritize frequently accessed items regardless of type', () => {
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// Add item with high access count, low rebuild cost
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cache.set('hot1', { data: 'hot' }, 'metadata', 100, 1)
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for (let i = 0; i < 100; i++) {
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cache.getSync('hot1')
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}
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// Add item with low access count, high rebuild cost
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cache.set('cold1', { data: 'cold' }, 'hnsw', 100, 50)
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// Only access once (implicit from set)
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// Fill cache
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cache.set('new1', { data: 'new' }, 'other', 900, 1)
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const stats = cache.getStats()
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// hot1 score: 101 * 1 = 101 (keep)
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// cold1 score: 1 * 50 = 50 (keep)
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// Both should be kept as they have reasonable scores
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// At least one should be present
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const hasHot = cache.getSync('hot1') !== undefined
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const hasCold = cache.getSync('cold1') !== undefined
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expect(hasHot || hasCold).toBe(true)
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expect(stats.itemCount).toBeGreaterThan(0)
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})
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it('should properly score items with varying rebuild costs', () => {
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const items = [
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{ key: 'cheap1', cost: 1, accesses: 1 }, // score: 1
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{ key: 'medium1', cost: 10, accesses: 1 }, // score: 10
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{ key: 'expensive1', cost: 100, accesses: 1 } // score: 100
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]
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// Add all items
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for (const item of items) {
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cache.set(item.key, { data: item.key }, 'other', 100, item.cost)
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}
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// Fill cache to force eviction
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cache.set('filler', { data: 'filler' }, 'other', 900, 1)
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// Expensive items (high rebuild cost) should be more likely to stay
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// Even with same access count, rebuild cost should matter
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const stats = cache.getStats()
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// Should have at least kept some items
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expect(stats.itemCount).toBeGreaterThan(0)
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// Expensive items should have priority
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const hasExpensive = cache.getSync('expensive1') !== undefined
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const hasCheap = cache.getSync('cheap1') !== undefined
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// If we have to choose, expensive should be kept over cheap
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if (stats.itemCount === 2) {
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expect(hasExpensive).toBe(true)
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}
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})
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it('should handle fairness eviction correctly', () => {
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// Add many metadata entries (create imbalance)
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for (let i = 0; i < 5; i++) {
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cache.set(`meta${i}`, { data: i }, 'metadata', 100, 1)
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}
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// Add one HNSW with high value
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cache.set('hnsw1', { data: 'vector' }, 'hnsw', 100, 50)
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for (let i = 0; i < 50; i++) {
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cache.getSync('hnsw1')
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}
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// Fill to capacity
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cache.set('filler', { data: 'fill' }, 'other', 400, 1)
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// HNSW should be protected despite being outnumbered
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expect(cache.getSync('hnsw1')).toBeDefined()
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})
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it('should evict items with lowest combined score first', () => {
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const testItems = [
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{ key: 'item1', accesses: 1, cost: 1 }, // score: 1
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{ key: 'item2', accesses: 5, cost: 2 }, // score: 10
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{ key: 'item3', accesses: 10, cost: 5 }, // score: 50
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]
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// Add items
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for (const item of testItems) {
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cache.set(item.key, { data: item.key }, 'other', 100, item.cost)
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for (let i = 1; i < item.accesses; i++) {
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cache.getSync(item.key)
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}
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}
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// Force eviction
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cache.set('large', { data: 'large' }, 'other', 800, 1)
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// Item with highest score should be most likely to survive
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const hasItem3 = cache.getSync('item3') !== undefined
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const hasItem1 = cache.getSync('item1') !== undefined
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// item3 (score 50) should be kept over item1 (score 1)
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if (hasItem3 || hasItem1) {
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expect(hasItem3).toBe(true)
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}
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})
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it('should maintain cache efficiency under load', () => {
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// Add many items with different characteristics
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for (let i = 0; i < 10; i++) {
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const cost = i % 3 === 0 ? 50 : 1 // Every 3rd item is expensive
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cache.set(`item${i}`, { data: i }, 'other', 50, cost)
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// Access expensive items more
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if (cost === 50) {
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for (let j = 0; j < 10; j++) {
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cache.getSync(`item${i}`)
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}
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}
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}
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const stats = cache.getStats()
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// Should have kept cache operational
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expect(stats.itemCount).toBeGreaterThan(0)
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expect(stats.itemCount).toBeLessThanOrEqual(10)
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// Expensive frequently-accessed items should be present
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let expensiveKept = 0
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for (let i = 0; i < 10; i++) {
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if (i % 3 === 0 && cache.getSync(`item${i}`)) {
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expensiveKept++
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}
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}
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expect(expensiveKept).toBeGreaterThan(0)
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})
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it('should handle metadata vs HNSW eviction scenario from bug report', () => {
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// Simulate the bug scenario:
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// - Metadata: 99.7% cache size, 3.7% access
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// - HNSW: Small cache size, high access
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// Add lots of metadata (cheap to rebuild)
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for (let i = 0; i < 8; i++) {
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cache.set(`meta${i}`, { data: i }, 'metadata', 100, 1)
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// Low access
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cache.getSync(`meta${i}`)
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}
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// Add HNSW vectors (expensive to rebuild)
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cache.set('hnsw1', { vector: [1, 2, 3] }, 'hnsw', 100, 50)
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cache.set('hnsw2', { vector: [4, 5, 6] }, 'hnsw', 100, 50)
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// High access to HNSW
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for (let i = 0; i < 100; i++) {
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cache.getSync('hnsw1')
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cache.getSync('hnsw2')
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}
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const stats = cache.getStats()
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// Calculate scores:
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// metadata: ~2 * 1 = 2 each
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// hnsw1: 101 * 50 = 5050
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// hnsw2: 101 * 50 = 5050
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// HNSW should be protected
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expect(cache.getSync('hnsw1')).toBeDefined()
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expect(cache.getSync('hnsw2')).toBeDefined()
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// Verify that HNSW has higher value than metadata
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// (even if all fit in cache, the scoring should be correct)
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let metadataCount = 0
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for (let i = 0; i < 8; i++) {
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if (cache.getSync(`meta${i}`)) {
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metadataCount++
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}
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}
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// Both HNSW vectors should be present (they're high value)
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// Metadata may or may not be evicted depending on cache size
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expect(metadataCount).toBeLessThanOrEqual(8)
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})
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})
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