simple

Simple Example - Getting Started with LedgerQ

⭐ Start here if you're new to LedgerQ!

This example demonstrates the core operations: open, enqueue, dequeue, and stats.

What You'll Learn

• Opening a queue with default configuration
• Enqueuing messages (writing to queue)
• Dequeuing messages (reading from queue)
• Checking queue statistics
• Proper cleanup with defer

Running the Example

go run main.go

Sample Output

LedgerQ Simple Example
======================

✓ Queue opened at: /tmp/ledgerq-simple-example

Enqueuing messages:
  1. Enqueued at offset 64: Hello, World!
  2. Enqueued at offset 107: This is LedgerQ
  3. Enqueued at offset 152: A persistent message queue
  4. Enqueued at offset 208: Written in Go

Queue Stats:
  Total messages:   4
  Pending messages: 4
  Segments:         1

Dequeuing messages:
  1. [ID:1] Hello, World!
  2. [ID:2] This is LedgerQ
  3. [ID:3] A persistent message queue
  4. [ID:4] Written in Go

Final Stats:
  Total messages:   4
  Pending messages: 0

✓ Example completed successfully!

Key Concepts

1. Opening a Queue

q, err := ledgerq.Open("/path/to/queue", nil)
if err != nil {
    log.Fatal(err)
}
defer q.Close()  // Always close when done

• First argument: directory path (created if doesn't exist)
• Second argument: nil uses default options
• Always close the queue with defer for proper cleanup

2. Enqueuing Messages

offset, err := q.Enqueue([]byte("Hello, World!"))

• Takes []byte payload (convert strings with []byte())
• Returns offset (unique ID for this message)
• Thread-safe - multiple goroutines can enqueue simultaneously

3. Dequeuing Messages

msg, err := q.Dequeue()
fmt.Printf("[ID:%d] %s\n", msg.ID, msg.Payload)

• Returns next unread message (FIFO order)
• msg.ID: Unique message identifier
• msg.Payload: Your data as []byte
• Read position persists across restarts

4. Queue Statistics

stats := q.Stats()
fmt.Printf("Total: %d, Pending: %d\n",
    stats.TotalMessages, stats.PendingMessages)

• TotalMessages: All messages ever enqueued
• PendingMessages: Unread messages waiting
• SegmentCount: Number of storage files

How It Works

┌─────────────┐
│  Enqueue()  │ → Write to disk → Append-only log
└─────────────┘                    ↓
                                [msg1][msg2][msg3][msg4]
                                   ↑
┌─────────────┐                   │
│  Dequeue()  │ ← Read from disk ←┘
└─────────────┘

1. Messages written sequentially to disk (append-only)
2. Each message gets unique monotonic ID
3. Read position tracks what's been consumed
4. Crash-safe: power loss won't lose data

Next Steps

Try these examples next:

• producer-consumer - Multiple goroutines
• ttl - Message expiration
• headers - Message metadata

Common Patterns

Error Handling

msg, err := q.Dequeue()
if err != nil {
    if err == ledgerq.ErrNoMessages {
        // Queue is empty - wait or retry
        time.Sleep(100 * time.Millisecond)
    } else {
        log.Fatal(err)
    }
}

Batch Processing

// Enqueue multiple messages at once (faster)
payloads := [][]byte{
    []byte("msg1"),
    []byte("msg2"),
    []byte("msg3"),
}
offsets, err := q.EnqueueBatch(payloads)

// Dequeue up to 10 messages
messages, err := q.DequeueBatch(10)

Temporary Queue

// Auto-cleanup on exit
queueDir := "/tmp/myqueue"
defer os.RemoveAll(queueDir)

q, _ := ledgerq.Open(queueDir, nil)
defer q.Close()

Troubleshooting

Queue won't open?

• Check directory permissions (needs write access)
• Verify path is valid
• Ensure disk space available

No messages when dequeuing?

• Queue might be empty (err == ledgerq.ErrNoMessages)
• Check stats.PendingMessages count

Want to reset?

• Close queue and delete directory: rm -rf /path/to/queue
• Reopening will create fresh queue

Configuration

This example uses defaults. For custom config:

opts := ledgerq.DefaultOptions("/path/to/queue")
opts.AutoSync = true              // Sync after each write (safer, slower)
opts.MaxSegmentSize = 100 * 1024 * 1024  // 100MB segments
q, err := ledgerq.Open("/path/to/queue", opts)

See docs/USAGE.md for all options.

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Difficulty: 🟢 Beginner | Time: 2 minutes | Lines of Code: ~40