# Size-Based Retention

Limit stream size by keeping only the last N events.

## Configuration

```csharp
var policy = new RetentionPolicyConfig
{
    StreamName = "analytics",
    MaxEventCount = 1_000_000,  // Keep last 1 million events
    Enabled = true
};

await _policyStore.SetPolicyAsync(policy);
```

## Use Cases

| Stream Type | Max Events | Reason |
|-------------|------------|---------|
| **Hot Analytics** | 100k-1M | Recent data only |
| **Sliding Window** | 10k-100k | Last N transactions |
| **Debug Logs** | 50k-500k | Recent errors |
| **Metrics** | 1M-10M | Time-series data |

## SQL Implementation

```sql
CREATE OR REPLACE FUNCTION apply_size_retention(
    p_stream_name TEXT,
    p_max_event_count INTEGER
) RETURNS INTEGER AS $$
DECLARE
    deleted_count INTEGER;
BEGIN
    DELETE FROM events
    WHERE stream_name = p_stream_name
      AND offset < (
          SELECT MAX(offset) - p_max_event_count
          FROM events
          WHERE stream_name = p_stream_name
      );

    GET DIAGNOSTICS deleted_count = ROW_COUNT;
    RETURN deleted_count;
END;
$$ LANGUAGE plpgsql;
```

## See Also

- [Retention Policies Overview](README.md)
- [Time-Based Retention](time-based-retention.md)