mc

Memcache Client for Go

A high-performance memcache client library for Go that uses memcache's Meta Text Protocol and supports namespacing, compression, and context cancellation out of the box.

Table of Contents

• Features
• Installation
• Quick Start
• Basic Operations
• Advanced Features
  • Cache Management
  • Concurrency & Consistency
  • Performance Optimization
• Configuration
• Error Handling
• Meta Text Protocol
• Development
• Examples
• Contributing
• License
• References

Features

• ✅ Meta Text Protocol - Full support for memcache's modern protocol
• ✅ Context Support - All operations support context.Context for cancellation and timeouts
• ✅ Namespacing - Built-in namespace support for cache invalidation
• ✅ Compression - Optional compression with configurable thresholds
• ✅ Connection Pooling - Efficient connection pooling with automatic management
• ✅ Binary Key Encoding - Optional binary key encoding for better performance
• ✅ Type Safety - Strong typing with comprehensive error handling
• ✅ Atomic Operations - Safe append, prepend, and replace operations
• ✅ Optimistic Locking - CAS (Compare-And-Swap) for concurrent updates
• ✅ Batch Operations - Efficient multi-key retrieval with GetMulti

Installation

go get github.com/kinescope/mc

Quick Start

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/kinescope/mc"
)

func main() {
	// Create a new client
	client, err := mc.New(&mc.Options{
		Addrs: []string{"127.0.0.1:11211"},
	})
	if err != nil {
		log.Fatal(err)
	}
	defer client.Close()

	ctx := context.Background()

	// Set a value
	err = client.Set(ctx, &mc.Item{
		Key:   "user:123",
		Value: []byte("John Doe"),
		Flags: 0,
	}, mc.WithExpiration(3600))
	if err != nil {
		log.Fatal(err)
	}

	// Get a value
	item, err := client.Get(ctx, "user:123")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("Value: %s\n", item.Value)
}

Basic Operations

Set, Get, Delete

ctx := context.Background()

// Set
err := client.Set(ctx, &mc.Item{
	Key:   "key",
	Value: []byte("value"),
}, mc.WithExpiration(60))

// Get
item, err := client.Get(ctx, "key")
if err != nil {
	if err == mc.ErrCacheMiss {
		// Key not found
	}
}

// Delete
err = client.Del(ctx, "key")

Add, Replace, Append, and Prepend

// Add (only if key doesn't exist)
err := client.Add(ctx, &mc.Item{
	Key:   "key",
	Value: []byte("value"),
})

// Replace (only if key exists)
err := client.Replace(ctx, &mc.Item{
	Key:   "key",
	Value: []byte("new value"),
})

// Append data to existing item
err := client.Append(ctx, &mc.Item{
	Key:   "key",
	Value: []byte(" appended"),
})

// Prepend data to existing item
err := client.Prepend(ctx, &mc.Item{
	Key:   "key",
	Value: []byte("prepended "),
})

// Append with autovivify (create if doesn't exist)
// WithExpiration enables autovivify for append/prepend operations
err := client.Append(ctx, &mc.Item{
	Key:   "key",
	Value: []byte("value"),
}, mc.WithExpiration(3600)) // Create with 1 hour TTL if missing

// Prepend with autovivify (create if doesn't exist)
err := client.Prepend(ctx, &mc.Item{
	Key:   "key",
	Value: []byte("prefix"),
}, mc.WithExpiration(3600)) // Create with 1 hour TTL if missing

Increment and Decrement

// Increment
newValue, err := client.Inc(ctx, "counter", 1, 3600, mc.WithInitialValue(0))

// Decrement
newValue, err := client.Dec(ctx, "counter", 1, 3600)

Get Multiple Keys

keys := []string{"key1", "key2", "key3"}
items, err := client.GetMulti(ctx, keys)
for key, item := range items {
	fmt.Printf("%s: %s\n", key, item.Value)
}

Advanced Features

Cache Management

Namespacing

Namespacing allows you to invalidate all cache entries for a namespace with a single operation. This is useful for cache invalidation by user, tenant, or any logical grouping.

ctx := context.Background()
userID := "123"

// Store items with namespace
err := client.Set(ctx, &mc.Item{
	Key:   "name",
	Value: []byte("John"),
}, mc.WithNamespace("user:"+userID))

err = client.Set(ctx, &mc.Item{
	Key:   "email",
	Value: []byte("[email protected]"),
}, mc.WithNamespace("user:"+userID))

// Invalidate all items for this user
err = client.PurgeNamespace(ctx, "user:"+userID)
// Both "name" and "email" keys are now invalidated

For more information, see the memcache namespacing documentation.

Compression

Enable compression for values larger than a specified threshold:

err := client.Set(ctx, &mc.Item{
	Key:   "large_data",
	Value: largeData,
}, mc.WithCompression(1024)) // Compress if value > 1KB

You can also provide custom compression functions:

client, err := mc.New(&mc.Options{
		Addrs: []string{"127.0.0.1:11211"},
	Compression: struct {
		Compress   func([]byte) ([]byte, error)
		Decompress func([]byte) ([]byte, error)
	}{
		Compress:   myCompress,
		Decompress: myDecompress,
	},
})

Min Uses

Require an item to be set a minimum number of times before it can be retrieved:

// Set with min uses
err := client.Set(ctx, &mc.Item{
	Key:   "key",
	Value: []byte("value"),
}, mc.WithMinUses(3))

// First 2 Get calls will return ErrCacheMiss
// After 3rd Set, Get will succeed

Concurrency & Consistency

Compare-and-Swap (Optimistic Locking)

Use CAS for safe concurrent updates:

// Get item with CAS value
item, err := client.Get(ctx, "key", mc.WithCAS())
if err == nil {
	// Modify the value
	item.Value = []byte("new value")
	// Update only if CAS matches (no concurrent modification)
	err = client.CompareAndSwap(ctx, item)
	if err == mc.ErrCASConflict {
		// Another client modified the item, retry
	}
}

CAS Override

For forced updates, use Set instead of CompareAndSwap:

// Set bypasses CAS check for forced updates
err := client.Set(ctx, &mc.Item{
	Key:   "key",
	Value: []byte("forced value"),
}, mc.WithExpiration(3600))

Performance Optimization

Early Recache & Stampeding Herd Prevention

Prevent cache stampede using early recache:

item, err := client.Get(ctx, "key", mc.WithEarlyRecache(60))
if item.Won() {
	// This client won the recache - refresh in background
	go refreshCache(ctx, client, "key")
} else {
	// Other clients get cached data immediately
	useCachedData(item.Value)
}

Serve Stale Data

Serve stale data when items have expired to prevent cache misses:

item, err := client.Get(ctx, "key", mc.WithEarlyRecache(60))
if item.Stale() {
	// Serve stale data while refreshing in background
	if item.Won() {
		go refreshCache(ctx, client, "key")
	}
	useData(item.Value)
}

Hot Key Detection & Management

Identify and manage frequently accessed (hot) cache keys. For hot keys, avoid deletion as it causes cache misses. Instead, update values in place or use early recache:

// Track hot keys using hit status and last access time
item, err := client.Get(ctx, "key", mc.WithHit(), mc.WithLastAccess())
if item.Hit() && item.LastAccess() < 10 {
	// Key is hot - update value without deletion to avoid cache misses
	// This keeps the key available while refreshing data
	client.Set(ctx, &mc.Item{
		Key:   "key",
		Value: freshData,
	}, mc.WithExpiration(3600))
	
	// Alternative: Use early recache for background refresh
	// The key remains available while being refreshed
}

Last Access Time

Get the time since last access for cache optimization:

item, err := client.Get(ctx, "key", mc.WithLastAccess())
fmt.Printf("Last accessed %d seconds ago\n", item.LastAccess())

Hit Tracking

Track hit status to identify frequently accessed items:

item, err := client.Get(ctx, "key", mc.WithHit())
if item.Hit() {
	// Key has been accessed before - consider it hot
	// Extend TTL, pre-warm, or monitor for optimization
}

Context and Timeouts

All operations support context.Context for cancellation and timeouts:

// With timeout
ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()

item, err := client.Get(ctx, "key")
	if err != nil {
	if err == context.DeadlineExceeded {
		// Operation timed out
	}
}

// With cancellation
ctx, cancel := context.WithCancel(context.Background())
go func() {
	time.Sleep(1 * time.Second)
	cancel() // Cancel the operation
}()
item, err := client.Get(ctx, "key")

Configuration

Client Options

client, err := mc.New(&mc.Options{
	// Server addresses
	Addrs: []string{"127.0.0.1:11211", "127.0.0.1:11212"},

	// Connection settings
	DialTimeout:         200 * time.Millisecond,
	ConnMaxLifetime:     time.Minute,
	MaxIdleConnsPerAddr: 10,

	// Disable binary key encoding (use plain text keys)
	DisableBinaryEncodedKeys: false,

	// Custom server selection function
	PickServer: func(key string) []string {
		// Custom logic to select servers
		return []string{"127.0.0.1:11211"}
	},

	// Custom compression
	Compression: struct {
		Compress   func([]byte) ([]byte, error)
		Decompress func([]byte) ([]byte, error)
	}{
		Compress:   gzip.Compress,
		Decompress: gzip.Decompress,
	},
})

Error Handling

The library provides typed errors for common scenarios:

item, err := client.Get(ctx, "key")
switch err {
case mc.ErrCacheMiss:
	// Key not found
case mc.ErrNotStored:
	// Item not stored (e.g., Add failed because key exists)
case mc.ErrCASConflict:
	// Compare-and-swap conflict
case mc.ErrMalformedKey:
	// Invalid key format
case mc.ErrNoServers:
	// No servers available
case nil:
	// Success
default:
	// Other error
}

Graceful Shutdown

Always close the client when done to release resources:

client, err := mc.New(&mc.Options{
	Addrs: []string{"127.0.0.1:11211"},
})
defer client.Close() // Closes all connections in the pool

Meta Text Protocol

This library uses memcache's Meta Text Protocol, a modern, efficient protocol that solves several problems with the traditional ASCII protocol:

Key Advantages

1. Reduced Network Overhead - More compact command format, fewer round trips
2. Atomic Operations - Safe append, prepend, and replace operations
3. Rich Metadata - CAS values, flags, TTL, last access time, hit status in a single request
4. Conditional Operations - Compare-and-Swap (CAS) for optimistic locking
5. Efficient Multi-Get - Batch key retrieval with the mn command
6. Early Recaching - Built-in support for preventing cache stampedes
7. Binary Key Support - Efficient binary-encoded keys
8. Opaque Values - Request/response correlation for async operations
9. Flexible Expiration - Update TTL without retrieving the value
10. Better Error Handling - Detailed error responses and status codes
11. Hot Key Detection - Hit tracking and last access time
12. Stale Data Serving - Serve expired data to prevent cache misses

Protocol Commands Used

• mg - Meta Get (retrieve items)
• ms - Meta Set (store items)
• ma - Meta Arithmetic (increment/decrement)
• md - Meta Delete (delete items)
• mn - Meta No-op (end of multi-get batch)

Development

Running Tests

# Run all tests
make test

# Run tests with race detector
make test-race

# Run tests with coverage
make test-coverage

# Run benchmarks
make test-bench

Code Quality

# Format code
make fmt

# Run linter
make lint

# Run all checks
make check

Generating Protobuf Code

make proto

Examples

See the example_test.go file for comprehensive examples including:

• Basic operations (Set, Get, Delete, Add, Replace, Append, Prepend)
• Compare-and-Swap operations
• Increment/Decrement with initial values
• Multi-key retrieval
• Namespace management
• Compression
• Early recache and stampeding herd prevention
• Serve stale data
• Hot key cache invalidation
• CAS consistency patterns
• Context and timeout handling

Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines.

License

This project is licensed under the MIT License - see the LICENSE file for details.

References

• Memcache Meta Text Protocol
• Memcache Namespacing
• Go Documentation