# Time-Based Retention

Delete events older than specified age.

## Configuration

```csharp
var policy = new RetentionPolicyConfig
{
    StreamName = "orders",
    MaxAge = TimeSpan.FromDays(90),  // Keep events for 90 days
    Enabled = true
};

await _policyStore.SetPolicyAsync(policy);
```

## Common Retention Periods

| Stream Type | Retention | Reason |
|-------------|-----------|---------|
| **Audit Logs** | 7 years | Compliance (SOX, GDPR) |
| **Order Events** | 90-365 days | Business analytics |
| **Analytics** | 30-90 days | Short-term insights |
| **Debug Logs** | 7-30 days | Troubleshooting |
| **Notifications** | 7-14 days | Recent history only |

## Usage Examples

### Compliance (7 Years)

```csharp
await _policyStore.SetPolicyAsync(new RetentionPolicyConfig
{
    StreamName = "audit-logs",
    MaxAge = TimeSpan.FromDays(365 * 7),  // 7 years
    Enabled = true
});
```

### Business Data (1 Year)

```csharp
await _policyStore.SetPolicyAsync(new RetentionPolicyConfig
{
    StreamName = "orders",
    MaxAge = TimeSpan.FromDays(365),  // 1 year
    Enabled = true
});
```

### Short-Term Logs (30 Days)

```csharp
await _policyStore.SetPolicyAsync(new RetentionPolicyConfig
{
    StreamName = "application-logs",
    MaxAge = TimeSpan.FromDays(30),  // 30 days
    Enabled = true
});
```

## SQL Implementation

```sql
CREATE OR REPLACE FUNCTION apply_time_retention(
    p_stream_name TEXT,
    p_max_age_seconds INTEGER
) RETURNS INTEGER AS $$
DECLARE
    deleted_count INTEGER;
BEGIN
    DELETE FROM events
    WHERE stream_name = p_stream_name
      AND timestamp < NOW() - (p_max_age_seconds || ' seconds')::INTERVAL;

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

## Monitoring

```csharp
public async Task<RetentionStats> GetRetentionStatsAsync(string streamName)
{
    var policy = await _policyStore.GetPolicyAsync(streamName);
    var oldestEvent = await GetOldestEventAsync(streamName);
    var eventsToDelete = await CountEventsOlderThanAsync(
        streamName,
        DateTimeOffset.UtcNow - policy.MaxAge);

    return new RetentionStats
    {
        OldestEventAge = DateTimeOffset.UtcNow - oldestEvent.Timestamp,
        EventsToDelete = eventsToDelete,
        RetentionPeriod = policy.MaxAge
    };
}
```

## See Also

- [Retention Policies Overview](README.md)
- [Size-Based Retention](size-based-retention.md)
- [Cleanup Windows](cleanup-windows.md)