Migration Guide

This guide helps you migrate from existing caching solutions to Rapp.

Table of Contents

• From JSON (System.Text.Json)
• From MemoryPack
• From Other Binary Serializers
• Handling Schema Evolution

---

From JSON (System.Text.Json)

Before (JSON)

public class UserData
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime CreatedAt { get; set; }
}

// Configure HybridCache with JSON
builder.Services.AddHybridCache(options =>
{
    // JSON is the default
});

// Usage
var cached = await cache.GetOrCreateAsync(
    "user-123",
    async ct => await GetUserDataAsync(123, ct)
);

After (Rapp)

using Rapp;
using MemoryPack;

[RappCache]  // Add this attribute
[MemoryPackable]  // Add this attribute
public partial class UserData  // Add 'partial' keyword
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime CreatedAt { get; set; }
}

// Configure HybridCache with Rapp
builder.Services.AddHybridCache(options =>
{
    // Options configuration
}).UseRappForUserData();  // Generated extension method

// Usage (same as before)
var cached = await cache.GetOrCreateAsync(
    "user-123",
    async ct => await GetUserDataAsync(123, ct)
);

Benefits

• 5.6× faster serialization, 17.9× faster deserialization
• 65% less memory usage
• Smaller cache payloads (70% smaller than JSON)
• Schema validation prevents crashes on deployments

---

From MemoryPack

Before (Direct MemoryPack)

[MemoryPackable]
public partial class CacheItem
{
    public int Id { get; set; }
    public string Value { get; set; }
}

// Custom serializer
public class MemoryPackHybridSerializer<T> : IHybridCacheSerializer<T>
{
    public void Serialize(T value, IBufferWriter<byte> target)
    {
        MemoryPackSerializer.Serialize(target, value);
    }

    public T Deserialize(ReadOnlySequence<byte> source)
    {
        return MemoryPackSerializer.Deserialize<T>(source);
    }
}

// Manual registration
builder.Services.AddHybridCache()
    .AddSerializer<CacheItem, MemoryPackHybridSerializer<CacheItem>>();

After (Rapp)

[RappCache]  // Add this attribute
[MemoryPackable]
public partial class CacheItem
{
    public int Id { get; set; }
    public string Value { get; set; }
}

// Automatic registration
builder.Services.AddHybridCache()
    .UseRappForCacheItem();  // Generated extension method

Benefits

• No custom serializer code - fully generated
• Schema validation prevents crashes on property changes
• Same performance as raw MemoryPack
• Safer deployments with automatic version checking

Important Differences

Schema Changes

MemoryPack - Crashes on schema mismatch:

// Old version
[MemoryPackable]
public partial class Item
{
    public int Id { get; set; }
}

// New version - CRASHES on old cached data!
[MemoryPackable]
public partial class Item
{
    public int Id { get; set; }
    public string Name { get; set; }  // Added property
}

Rapp - Handles schema changes gracefully:

// Old version
[RappCache]
[MemoryPackable]
public partial class Item
{
    public int Id { get; set; }
}

// New version - Returns default, cache rebuilds automatically
[RappCache]
[MemoryPackable]
public partial class Item
{
    public int Id { get; set; }
    public string Name { get; set; }  // Schema mismatch detected, returns default
}

---

From Other Binary Serializers

From Protobuf-net

// Before
[ProtoContract]
public class MyData
{
    [ProtoMember(1)]
    public int Id { get; set; }
}

// After
[RappCache]
[MemoryPackable]
public partial class MyData
{
    public int Id { get; set; }
}

From MessagePack

// Before
[MessagePackObject]
public class MyData
{
    [Key(0)]
    public int Id { get; set; }
}

// After
[RappCache]
[MemoryPackable]
public partial class MyData
{
    public int Id { get; set; }
}

---

Handling Schema Evolution

Deployment Strategy

1. Add New Properties with Defaults

   [RappCache]
   [MemoryPackable]
   public partial class User
   {
       public int Id { get; set; }
       public string Name { get; set; }
       public string? Email { get; set; } = null;  // Safe to add
   }

2. Use Nullable Types for Optional Data

   [RappCache]
   [MemoryPackable]
   public partial class Order
   {
       public int Id { get; set; }
       public DateTime? ProcessedAt { get; set; }  // Nullable
   }

3. Clear Cache on Breaking Changes

   // Option 1: Clear specific cache entries
   await cache.RemoveAsync("user-*");
   
   // Option 2: Use versioned keys
   var key = $"v2:user-{userId}";  // Version prefix

Schema Change Detection

Rapp automatically detects schema changes and returns default(T):

// Old cached data exists
var result = await cache.GetOrCreateAsync(
    "data-key",
    async ct => await FetchDataAsync(ct)
);

// If schema changed:
// - Old data is rejected (returns default)
// - Factory function is called
// - New data with new schema is cached

Monitoring Schema Mismatches

// Enable telemetry to track schema mismatches
RappConfiguration.EnableTelemetry = true;

// Metrics available:
// - rapp_cache_hits_total
// - rapp_cache_misses_total
// - rapp_schema_mismatches_total (when enabled)

---

Configuration Options

Global Configuration

// Disable telemetry
RappConfiguration.EnableTelemetry = false;

// Enable detailed errors (development only)
RappConfiguration.EnableDetailedErrors = true;

// Throw exceptions on schema mismatch (testing only)
RappConfiguration.ThrowOnSchemaMismatch = true;

Per-Type Configuration

Generated extension methods provide type-safe registration:

builder.Services.AddHybridCache()
    .UseRappForUser()        // For User class
    .UseRappForProduct()     // For Product class
    .UseRappForOrder();      // For Order class

---

Performance Comparison

Scenario	JSON	MemoryPack	Rapp	Notes
Serialize	1,764.1 ns	197.0 ns	397.2 ns	Rapp overhead: ~102%
Deserialize	4,238.1 ns	180.0 ns	240.9 ns	Rapp overhead: ~34%
vs JSON	1.0×	9.0× faster (ser)	4.4× faster (ser)	Rapp: 17.6× faster (deser)
HybridCache	N/A	416.5 ns	436.9 ns	Rapp overhead: ~4.9%
Realistic (100 ops)	N/A	44.1 μs	30.5 μs	Rapp 31% faster!
Schema Safety				Rapp matches JSON
AOT Compatible				Rapp matches MemoryPack

Benchmarks: .NET 10.0.1, Intel Core i7-4980HQ @ 2.80GHz, macOS. See benchmarks/ for details.

---

Troubleshooting

Issue: "Type is not MemoryPackable"

Solution: Add both attributes:

[RappCache]
[MemoryPackable]
public partial class MyClass { }

Issue: "Serializer not generated"

Cause: Missing partial keyword

Solution:

// Wrong
[RappCache]
public class MyClass { }

// Correct
[RappCache]
public partial class MyClass { }

Issue: Getting default values after deployment

Cause: Schema changed, old cache data rejected

Solution: This is expected behavior. Cache will rebuild with new schema.

---

Best Practices

1. Always use partial classes
2. Add properties as nullable when possible
3. Use versioned cache keys for breaking changes
4. Monitor schema mismatch metrics
5. Test deployments with schema changes
6. Keep telemetry enabled in production

---

Need Help?

• Check the Documentation
• View Examples
• Open an Issue
• Read the FAQ