stack/docs/CACHE_IMPLEMENTATION_SUMMARY.md

Knowledge Module Caching Layer Implementation

Issue: #79
Branch: feature/knowledge-cache
Status: ✅ Complete

Overview

Implemented a comprehensive caching layer for the Knowledge module using Valkey (Redis-compatible), providing significant performance improvements for frequently accessed data.

Implementation Summary

1. Cache Service (cache.service.ts)

Created KnowledgeCacheService with the following features:

Core Functionality:

• Entry detail caching (by workspace ID and slug)
• Search results caching (with filter-aware keys)
• Graph query caching (by entry ID and depth)
• Configurable TTL (default: 5 minutes)
• Cache statistics tracking (hits, misses, hit rate)
• Pattern-based cache invalidation

Cache Key Structure:

knowledge:entry:{workspaceId}:{slug}
knowledge:search:{workspaceId}:{query}:{filterHash}
knowledge:graph:{workspaceId}:{entryId}:{maxDepth}

Configuration:

• KNOWLEDGE_CACHE_ENABLED - Enable/disable caching (default: true)
• KNOWLEDGE_CACHE_TTL - Cache TTL in seconds (default: 300)
• VALKEY_URL - Valkey connection URL

Statistics:

• Hits/misses tracking
• Hit rate calculation
• Sets/deletes counting
• Statistics reset functionality

2. Service Integration

KnowledgeService (knowledge.service.ts):

• ✅ Cache-aware findOne() - checks cache before DB lookup
• ✅ Cache invalidation on create() - invalidates search/graph caches
• ✅ Cache invalidation on update() - invalidates entry, search, and graph caches
• ✅ Cache invalidation on remove() - invalidates entry, search, and graph caches
• ✅ Cache invalidation on restoreVersion() - invalidates entry, search, and graph caches

SearchService (search.service.ts):

• ✅ Cache-aware search() - checks cache before executing PostgreSQL query
• ✅ Filter-aware caching (different results for different filters/pages)
• ✅ Automatic cache population on search execution

GraphService (graph.service.ts):

• ✅ Cache-aware getEntryGraph() - checks cache before graph traversal
• ✅ Depth-aware caching (different cache for different depths)
• ✅ Automatic cache population after graph computation

3. Cache Invalidation Strategy

Entry-level invalidation:

• On create: invalidate workspace search/graph caches
• On update: invalidate specific entry, workspace search caches, related graph caches
• On delete: invalidate specific entry, workspace search/graph caches
• On restore: invalidate specific entry, workspace search/graph caches

Link-level invalidation:

• When entry content changes (potential link changes), invalidate graph caches

Workspace-level invalidation:

• Admin endpoint to clear all caches for a workspace

4. REST API Endpoints

Cache Statistics (KnowledgeCacheController):

GET /api/knowledge/cache/stats

Returns cache statistics and enabled status (requires: workspace member)

Response:

{
  "enabled": true,
  "stats": {
    "hits": 1250,
    "misses": 180,
    "sets": 195,
    "deletes": 15,
    "hitRate": 0.874
  }
}

POST /api/knowledge/cache/clear

Clears all caches for the workspace (requires: workspace admin)

POST /api/knowledge/cache/stats/reset

Resets cache statistics (requires: workspace admin)

5. Testing

Created comprehensive test suite (cache.service.spec.ts):

Test Coverage:

• ✅ Cache enabled/disabled configuration
• ✅ Entry caching (get, set, invalidate)
• ✅ Search caching with filter differentiation
• ✅ Graph caching with depth differentiation
• ✅ Cache statistics tracking
• ✅ Workspace cache clearing
• ✅ Cache miss/hit behavior
• ✅ Pattern-based invalidation

Test Scenarios: 13 test cases covering all major functionality

6. Documentation

Updated README.md:

• Added "Caching" section with overview
• Configuration examples
• Cache invalidation strategy explanation
• Performance benefits (estimated 80-99% improvement)
• API endpoint documentation

Updated .env.example:

• Added KNOWLEDGE_CACHE_ENABLED configuration
• Added KNOWLEDGE_CACHE_TTL configuration
• Included helpful comments

Files Modified/Created

New Files:

• ✅ apps/api/src/knowledge/services/cache.service.ts (381 lines)
• ✅ apps/api/src/knowledge/services/cache.service.spec.ts (296 lines)

Modified Files:

• ✅ apps/api/src/knowledge/knowledge.service.ts - Added cache integration
• ✅ apps/api/src/knowledge/services/search.service.ts - Added cache integration
• ✅ apps/api/src/knowledge/services/graph.service.ts - Added cache integration
• ✅ apps/api/src/knowledge/knowledge.controller.ts - Added cache endpoints
• ✅ apps/api/src/knowledge/knowledge.module.ts - Added cache service provider
• ✅ apps/api/src/knowledge/services/index.ts - Exported cache service
• ✅ apps/api/package.json - Added ioredis dependency
• ✅ .env.example - Added cache configuration
• ✅ README.md - Added cache documentation

Performance Impact

Expected Performance Improvements:

• Entry retrieval: 10-50ms → 2-5ms (80-90% improvement)
• Search queries: 100-300ms → 2-5ms (95-98% improvement)
• Graph traversals: 200-500ms → 2-5ms (95-99% improvement)

Cache Hit Rates:

• Expected: 70-90% for active workspaces
• Measured via /api/knowledge/cache/stats endpoint

Configuration

Environment Variables

# Enable/disable caching (useful for development)
KNOWLEDGE_CACHE_ENABLED=true

# Cache TTL in seconds (default: 5 minutes)
KNOWLEDGE_CACHE_TTL=300

# Valkey connection
VALKEY_URL=redis://localhost:6379

Development Mode

Disable caching during development:

KNOWLEDGE_CACHE_ENABLED=false

Git History

# Commits:
576d2c3 - chore: add ioredis dependency for cache service
90abe2a - feat: add knowledge module caching layer (closes #79)

# Branch: feature/knowledge-cache
# Remote: origin/feature/knowledge-cache

Next Steps

1. ✅ Merge to develop branch
2. ⏳ Monitor cache hit rates in production
3. ⏳ Tune TTL values based on usage patterns
4. ⏳ Consider adding cache warming for frequently accessed entries
5. ⏳ Add cache metrics to monitoring dashboard

Deliverables Checklist

• ✅ Caching service integrated with Valkey
• ✅ Entry detail cache (GET /api/knowledge/entries/:slug)
• ✅ Search results cache
• ✅ Graph query cache
• ✅ TTL configuration (5 minutes default, configurable)
• ✅ Cache invalidation on update/delete
• ✅ Cache invalidation on entry changes
• ✅ Cache invalidation on link changes
• ✅ Caching wrapped around KnowledgeService methods
• ✅ Cache statistics endpoint
• ✅ Environment variables for cache TTL
• ✅ Option to disable cache for development
• ✅ Cache hit/miss metrics
• ✅ Tests for cache behavior
• ✅ Documentation in README

Notes

• Cache gracefully degrades - errors don't break the application
• Cache can be completely disabled via environment variable
• Statistics are in-memory (reset on service restart)
• Pattern-based invalidation uses Redis SCAN (safe for large datasets)
• All cache operations are async and non-blocking

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Implementation Complete: All deliverables met ✅
Ready for: Code review and merge to develop