debug-cache

---

name: debug-cache description: Debug HybridCache and Redis caching issues when data isn't being cached or invalidated correctly. Use this when cache hit/miss rates are wrong.

Use this guide to troubleshoot HybridCache and Redis caching issues.

Quick Path (80% of issues)

// turbo

1. Check Redis is running:

   Copydocker ps | grep redis && redis-cli ping
   

   Should see: PONG

2. Check cache tags match between GetOrCreateAsync and RemoveByTagAsync

3. Check cache key includes all params (page, culture, userId)

4. Check RemoveByTagAsync is called after mutations

If still broken, continue to full debugging below.

---

Symptoms

• ✗ Data not being cached (always fetching from DB)
• ✗ Stale data after updates (cache not invalidating)
• ✗ Cache misses when should be hits
• ✗ Redis connection errors

Related Skills

Prerequisites:

• /start-solution - Solution must be running to debug cache

First Steps:

• /verify-feature - Run basic checks before caching-specific debugging

Related Debugging:

• /debug-sse - If issue seems SSE-related instead of cache
• /doctor - Verify Docker and Redis are installed

After Fixing:

• /verify-feature - Confirm caching works correctly
• /scaffold-test - Add tests for cache scenarios

Debugging Steps

1. Verify Cache Configuration

Check appsettings.json for cache settings:

Copy{
  "ConnectionStrings": {
    "cache": "localhost:6379"  // Redis connection string
  }
}

Test Redis connection:

Copy# Check if Redis is running
docker ps | grep redis

# Test connection
redis-cli ping
# Expected: PONG

If Redis isn't running:

• Start via Aspire: aspire run
• Or manually: docker run -p 6379:6379 redis:latest

2. Verify HybridCache Setup

Check Program.cs in ApiService:

Copy// ✅ Correct - HybridCache configured
builder.Services.AddHybridCache(options =>
{
    options.DefaultEntryOptions = new HybridCacheEntryOptions
    {
        Expiration = TimeSpan.FromMinutes(5),
        LocalCacheExpiration = TimeSpan.FromMinutes(1)
    };
});

// Add Redis (if using distributed cache)
builder.Services.AddStackExchangeRedisCache(options =>
{
    options.Configuration = builder.Configuration.GetConnectionString("cache");
});

// ✗ Wrong - missing configuration
// (no AddHybridCache call)

3. Verify Cache Usage in Code

Check endpoint is using cache:

Copy// ✅ Correct - using cache with tags
public static async Task<IResult> GetBooks(
    IDocumentStore store,
    HybridCache cache,  // ✅ Injected
    CancellationToken cancellationToken = default)
{
    var books = await cache.GetOrCreateAsync(
        "books:list",  // Cache key
        async entry =>
        {
            entry.SetOptions(new HybridCacheEntryOptions
            {
                Expiration = TimeSpan.FromMinutes(5)
            });

            await using var session = store.QuerySession();
            return await session.Query<BookProjection>().ToListAsync();
        },
        tags: [CacheTags.BookList],  // ✅ Tags for invalidation
        cancellationToken: cancellationToken
    );

    return Results.Ok(books);
}

// ✗ Wrong - no caching
public static async Task<IResult> GetBooks(
    IDocumentStore store,
    CancellationToken cancellationToken = default)
{
    await using var session = store.QuerySession();
    var books = await session.Query<BookProjection>().ToListAsync();
    return Results.Ok(books);
}

4. Verify Cache Invalidation

Check cache is invalidated after mutations:

Copy// In Handler or Endpoint
public static async Task<IResult> UpdateBook(
    UpdateBookCommand cmd,
    IDocumentSession session,
    HybridCache cache,
    CancellationToken cancellationToken)
{
    // ... mutation logic ...

    // ✅ Correct - invalidate by tag
    await cache.RemoveByTagAsync(CacheTags.BookList, cancellationToken);

    return Results.Ok();
}

// ✗ Wrong - cache never invalidated
// (no RemoveByTagAsync call)

5. Check Cache Tags Definition

Verify cache tags are defined in constants:

Copy// src/ApiService/BookStore.ApiService/Infrastructure/CacheTags.cs
public static class CacheTags
{
    public const string BookList = "book-list";
    public const string BookDetails = "book-details";
    public const string AuthorList = "author-list";

    // ❌ Missing: Your resource tags
}

If tags are missing:

1. Add const string for your resource
2. Use consistent naming pattern
3. Use tags in both GetOrCreateAsync and RemoveByTagAsync

6. Verify Cache Keys Include All Parameters

Cache keys must include all query parameters:

Copy// ✅ Correct - includes page, pageSize, culture
var cacheKey = $"books:page:{page}:size:{pageSize}:culture:{culture}";

var books = await cache.GetOrCreateAsync(
    cacheKey,
    async entry => { /* fetch data */ },
    tags: [CacheTags.BookList],
    cancellationToken: cancellationToken
);

// ✗ Wrong - missing parameters (same key for different pages)
var cacheKey = "books:list";  // Doesn't include page/size!

7. Test Cache Behavior

Test cache hit:

Copy# Request 1 - cache miss
curl http://localhost:5000/api/books

# Request 2 - should be cache hit (faster)
curl http://localhost:5000/api/books

Measure response times:

• First request: ~100-500ms (DB query)
• Second request: ~1-10ms (cache hit)

If both requests are slow:

• Cache isn't working
• Check HybridCache configuration
• Verify cache key is consistent

8. Check Redis with redis-cli

Connect to Redis and inspect:

Copy# Connect to Redis
redis-cli

# List all keys
KEYS *

# Get cache entry (if using Redis serialization)
GET "books:list"

# Check TTL (time to live)
TTL "books:list"

# Flush all cache (for testing)
FLUSHALL

9. Monitor Cache Metrics

Check Aspire Dashboard:

1. Go to Traces
2. Look for cache operations
3. Check hit/miss rates
4. Monitor cache latency

Add logging to debug:

Copypublic static async Task<IResult> GetBooks(
    IDocumentStore store,
    HybridCache cache,
    ILogger<Program> logger,  // Add logger
    CancellationToken cancellationToken = default)
{
    logger.LogInformation("Fetching books from cache");

    var books = await cache.GetOrCreateAsync(
        "books:list",
        async entry =>
        {
            logger.LogInformation("Cache MISS - fetching from DB");
            await using var session = store.QuerySession();
            return await session.Query<BookProjection>().ToListAsync();
        },
        tags: [CacheTags.BookList],
        cancellationToken: cancellationToken
    );

    logger.LogInformation("Returning {Count} books", books.Count);
    return Results.Ok(books);
}

Common Issues & Fixes

Issue: Cache Always Misses

Symptom: Every request fetches from DB

Diagnosis:

1. Add logging to cache callback (see above)
2. Check if callback always executes

Fixes:

• Verify Redis is running and connected
• Check cache key is consistent across requests
• Ensure HybridCache is registered in DI
• Verify no exceptions in cache retrieval

Issue: Stale Data After Updates

Symptom: Updates don't reflect until cache expires

Diagnosis:

1. Check if RemoveByTagAsync is called
2. Verify tags match between get and invalidate

Fixes:

Copy// ✅ Correct - matching tags
await cache.GetOrCreateAsync("key", ..., tags: [CacheTags.BookList]);
await cache.RemoveByTagAsync(CacheTags.BookList);

// ✗ Wrong - mismatched tags
await cache.GetOrCreateAsync("key", ..., tags: [CacheTags.BookList]);
await cache.RemoveByTagAsync(CacheTags.BookDetails);  // Wrong tag!

Issue: Different Users See Same Data (Cache Poisoning)

Symptom: User A sees User B's data

Diagnosis:

• Cache key doesn't include user ID or culture

Fix:

Copy// ✅ Correct - user-specific cache key
var userId = httpContext.User.FindFirst("sub")?.Value;
var cacheKey = $"cart:{userId}";

// ✗ Wrong - shared cache key
var cacheKey = "cart";  // Same for all users!

Issue: Redis Connection Errors

Symptom: StackExchange.Redis.RedisConnectionException

Diagnosis:

1. Check Redis container status: docker ps | grep redis
2. Verify connection string in appsettings.json
3. Check network between app and Redis

Fixes:

• Restart Redis container
• Check firewall rules
• Verify Aspire resource configuration in AppHost

Issue: Localized Data Not Cached Correctly

Symptom: Wrong language data returned

Diagnosis:

• Cache key doesn't include culture

Fix:

Copy// ✅ Correct - culture in cache key
var culture = CultureInfo.CurrentUICulture.Name;
var cacheKey = $"books:list:culture:{culture}";

// ✗ Wrong - missing culture
var cacheKey = "books:list";

Issue: Memory Leak

Symptom: Memory grows over time

Diagnosis:

• Cache expiration too long
• Too many unique cache keys

Fixes:

Copy// ✅ Correct - reasonable expiration
entry.SetOptions(new HybridCacheEntryOptions
{
    Expiration = TimeSpan.FromMinutes(5),        // Distributed cache
    LocalCacheExpiration = TimeSpan.FromMinutes(1)  // In-memory cache
});

// ✗ Wrong - cache never expires
entry.SetOptions(new HybridCacheEntryOptions
{
    Expiration = TimeSpan.MaxValue  // Never expires!
});

Verification Checklist

• Redis container is running (docker ps)
• Connection string configured in appsettings.json
• AddHybridCache() called in Program.cs
• Cache injected in endpoint (HybridCache cache)
• Cache key includes all query parameters
• Cache tags defined and used consistently
• RemoveByTagAsync called after mutations
• Cache expiration times are reasonable
• Logging added to debug cache behavior
• Metrics monitored in Aspire dashboard

Debugging Tools

Redis CLI:

Copyredis-cli
> KEYS *              # List all keys
> GET "key"           # Get value
> TTL "key"           # Check expiration
> FLUSHALL           # Clear all cache

Aspire Dashboard:

• Traces → Look for cache operations
• Metrics → Monitor hit/miss rates
• Logs → Search for cache-related errors

Logging:

Copylogger.LogInformation("Cache key: {Key}", cacheKey);
logger.LogInformation("Cache tags: {Tags}", string.Join(", ", tags));
logger.LogInformation("Cache callback executed (MISS)");

Performance Tips

• ✅ Use short local cache TTL (1-2 minutes)
• ✅ Use longer distributed cache TTL (5-15 minutes)
• ✅ Include culture in cache keys for localized data
• ✅ Use tag-based invalidation for complex scenarios
• ✅ Monitor cache hit rates (target: >80%)
• ❌ Don't cache user-specific data without user ID in key
• ❌ Don't use very long expirations (causes stale data)

Related Skills

First Steps:

• /verify-feature - Run basic checks before caching-specific debugging

Related Debugging:

• /debug-sse - If issue seems SSE-related instead of cache
• /doctor - Verify Docker and Redis are installed

After Fixing:

• /verify-feature - Confirm caching works correctly
• /scaffold-test - Add tests for cache scenarios

See Also:

• scaffold-read - Cache implementation patterns
• scaffold-write - Cache invalidation on mutations
• caching-guide - HybridCache configuration and patterns
• ApiService AGENTS.md - HybridCache configuration