docs: add cache implementation summary
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Jason Woltje
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CACHE_IMPLEMENTATION_SUMMARY.md
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CACHE_IMPLEMENTATION_SUMMARY.md
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# Knowledge Module Caching Layer Implementation
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**Issue:** #79
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**Branch:** `feature/knowledge-cache`
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**Status:** ✅ Complete
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## Overview
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Implemented a comprehensive caching layer for the Knowledge module using Valkey (Redis-compatible), providing significant performance improvements for frequently accessed data.
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## Implementation Summary
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### 1. Cache Service (`cache.service.ts`)
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Created `KnowledgeCacheService` with the following features:
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**Core Functionality:**
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- Entry detail caching (by workspace ID and slug)
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- Search results caching (with filter-aware keys)
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- Graph query caching (by entry ID and depth)
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- Configurable TTL (default: 5 minutes)
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- Cache statistics tracking (hits, misses, hit rate)
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- Pattern-based cache invalidation
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**Cache Key Structure:**
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```
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knowledge:entry:{workspaceId}:{slug}
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knowledge:search:{workspaceId}:{query}:{filterHash}
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knowledge:graph:{workspaceId}:{entryId}:{maxDepth}
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```
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**Configuration:**
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- `KNOWLEDGE_CACHE_ENABLED` - Enable/disable caching (default: true)
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- `KNOWLEDGE_CACHE_TTL` - Cache TTL in seconds (default: 300)
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- `VALKEY_URL` - Valkey connection URL
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**Statistics:**
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- Hits/misses tracking
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- Hit rate calculation
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- Sets/deletes counting
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- Statistics reset functionality
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### 2. Service Integration
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**KnowledgeService (`knowledge.service.ts`):**
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- ✅ Cache-aware `findOne()` - checks cache before DB lookup
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- ✅ Cache invalidation on `create()` - invalidates search/graph caches
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- ✅ Cache invalidation on `update()` - invalidates entry, search, and graph caches
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- ✅ Cache invalidation on `remove()` - invalidates entry, search, and graph caches
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- ✅ Cache invalidation on `restoreVersion()` - invalidates entry, search, and graph caches
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**SearchService (`search.service.ts`):**
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- ✅ Cache-aware `search()` - checks cache before executing PostgreSQL query
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- ✅ Filter-aware caching (different results for different filters/pages)
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- ✅ Automatic cache population on search execution
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**GraphService (`graph.service.ts`):**
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- ✅ Cache-aware `getEntryGraph()` - checks cache before graph traversal
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- ✅ Depth-aware caching (different cache for different depths)
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- ✅ Automatic cache population after graph computation
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### 3. Cache Invalidation Strategy
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**Entry-level invalidation:**
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- On create: invalidate workspace search/graph caches
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- On update: invalidate specific entry, workspace search caches, related graph caches
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- On delete: invalidate specific entry, workspace search/graph caches
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- On restore: invalidate specific entry, workspace search/graph caches
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**Link-level invalidation:**
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- When entry content changes (potential link changes), invalidate graph caches
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**Workspace-level invalidation:**
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- Admin endpoint to clear all caches for a workspace
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### 4. REST API Endpoints
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**Cache Statistics (`KnowledgeCacheController`):**
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```http
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GET /api/knowledge/cache/stats
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```
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Returns cache statistics and enabled status (requires: workspace member)
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**Response:**
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```json
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{
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"enabled": true,
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"stats": {
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"hits": 1250,
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"misses": 180,
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"sets": 195,
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"deletes": 15,
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"hitRate": 0.874
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}
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}
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```
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```http
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POST /api/knowledge/cache/clear
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```
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Clears all caches for the workspace (requires: workspace admin)
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```http
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POST /api/knowledge/cache/stats/reset
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```
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Resets cache statistics (requires: workspace admin)
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### 5. Testing
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Created comprehensive test suite (`cache.service.spec.ts`):
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**Test Coverage:**
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- ✅ Cache enabled/disabled configuration
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- ✅ Entry caching (get, set, invalidate)
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- ✅ Search caching with filter differentiation
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- ✅ Graph caching with depth differentiation
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- ✅ Cache statistics tracking
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- ✅ Workspace cache clearing
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- ✅ Cache miss/hit behavior
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- ✅ Pattern-based invalidation
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**Test Scenarios:** 13 test cases covering all major functionality
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### 6. Documentation
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**Updated README.md:**
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- Added "Caching" section with overview
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- Configuration examples
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- Cache invalidation strategy explanation
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- Performance benefits (estimated 80-99% improvement)
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- API endpoint documentation
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**Updated .env.example:**
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- Added `KNOWLEDGE_CACHE_ENABLED` configuration
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- Added `KNOWLEDGE_CACHE_TTL` configuration
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- Included helpful comments
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## Files Modified/Created
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### New Files:
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- ✅ `apps/api/src/knowledge/services/cache.service.ts` (381 lines)
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- ✅ `apps/api/src/knowledge/services/cache.service.spec.ts` (296 lines)
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### Modified Files:
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- ✅ `apps/api/src/knowledge/knowledge.service.ts` - Added cache integration
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- ✅ `apps/api/src/knowledge/services/search.service.ts` - Added cache integration
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- ✅ `apps/api/src/knowledge/services/graph.service.ts` - Added cache integration
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- ✅ `apps/api/src/knowledge/knowledge.controller.ts` - Added cache endpoints
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- ✅ `apps/api/src/knowledge/knowledge.module.ts` - Added cache service provider
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- ✅ `apps/api/src/knowledge/services/index.ts` - Exported cache service
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- ✅ `apps/api/package.json` - Added ioredis dependency
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- ✅ `.env.example` - Added cache configuration
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- ✅ `README.md` - Added cache documentation
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## Performance Impact
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**Expected Performance Improvements:**
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- Entry retrieval: 10-50ms → 2-5ms (80-90% improvement)
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- Search queries: 100-300ms → 2-5ms (95-98% improvement)
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- Graph traversals: 200-500ms → 2-5ms (95-99% improvement)
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**Cache Hit Rates:**
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- Expected: 70-90% for active workspaces
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- Measured via `/api/knowledge/cache/stats` endpoint
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## Configuration
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### Environment Variables
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```bash
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# Enable/disable caching (useful for development)
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KNOWLEDGE_CACHE_ENABLED=true
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# Cache TTL in seconds (default: 5 minutes)
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KNOWLEDGE_CACHE_TTL=300
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# Valkey connection
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VALKEY_URL=redis://localhost:6379
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```
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### Development Mode
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Disable caching during development:
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```bash
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KNOWLEDGE_CACHE_ENABLED=false
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```
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## Git History
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```bash
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# Commits:
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576d2c3 - chore: add ioredis dependency for cache service
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90abe2a - feat: add knowledge module caching layer (closes #79)
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# Branch: feature/knowledge-cache
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# Remote: origin/feature/knowledge-cache
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```
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## Next Steps
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1. ✅ Merge to develop branch
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2. ⏳ Monitor cache hit rates in production
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3. ⏳ Tune TTL values based on usage patterns
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4. ⏳ Consider adding cache warming for frequently accessed entries
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5. ⏳ Add cache metrics to monitoring dashboard
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## Deliverables Checklist
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- ✅ Caching service integrated with Valkey
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- ✅ Entry detail cache (GET /api/knowledge/entries/:slug)
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- ✅ Search results cache
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- ✅ Graph query cache
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- ✅ TTL configuration (5 minutes default, configurable)
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- ✅ Cache invalidation on update/delete
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- ✅ Cache invalidation on entry changes
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- ✅ Cache invalidation on link changes
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- ✅ Caching wrapped around KnowledgeService methods
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- ✅ Cache statistics endpoint
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- ✅ Environment variables for cache TTL
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- ✅ Option to disable cache for development
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- ✅ Cache hit/miss metrics
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- ✅ Tests for cache behavior
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- ✅ Documentation in README
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## Notes
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- Cache gracefully degrades - errors don't break the application
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- Cache can be completely disabled via environment variable
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- Statistics are in-memory (reset on service restart)
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- Pattern-based invalidation uses Redis SCAN (safe for large datasets)
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- All cache operations are async and non-blocking
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---
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**Implementation Complete:** All deliverables met ✅
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**Ready for:** Code review and merge to develop
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