Quick Reference: Durability Configuration

TL;DR 🎯

Production: Keep default (flush = true)
Testing: Set FlushEventsImmediately = false for speed

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Configuration

// Production (default) - Maximum safety
builder.Services.AddOpossum(options =>
{
    options.RootPath = "D:\\Database";
    options.UseStore("Production");
    // FlushEventsImmediately = true (default)
});

// Testing - Skip flush for speed
builder.Services.AddOpossum(options =>
{
    options.RootPath = "TestData";
    options.UseStore("TestContext");
    options.FlushEventsImmediately = false; // ← 2-3x faster tests
});

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What Gets Flushed?

Data Type	Flush?	Why
Events	✅ YES	Source of truth
Ledger	✅ YES	Sequence integrity
Projections	❌ NO	Rebuildable
Indices	❌ NO	Rebuildable

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Performance Impact

With Flush (Production):

• Event append: ~1-5ms
• Throughput: ~200-1000 events/sec (NVMe SSD)
• Guaranteed durability ✅

Without Flush (Testing):

• Event append: ~0.1-0.5ms
• Throughput: ~2000-10000 events/sec
• Risk of data loss ⚠️

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Decision Tree

Do you need guaranteed durability?
├─ YES (production) → Keep default (flush = true)
├─ NO (testing) → Set FlushEventsImmediately = false
└─ UNSURE → Use default (safe choice)

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When to Disable Flush

✅ Safe to disable:

• Unit tests
• Integration tests
• Local development
• Throwaway data

❌ NEVER disable in:

• Production
• Staging (if mirrors production)
• Any environment with important data

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Example: Test Configuration

public class TestFixture
{
    private readonly IEventStore _eventStore;
    
    public TestFixture()
    {
        var options = new OpossumOptions
        {
            RootPath = Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString()),
            FlushEventsImmediately = false // ← Faster tests
        };
        options.UseStore("TestContext");
        
        _eventStore = new FileSystemEventStore(options);
    }
}

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Troubleshooting

Tests Slower After Upgrade?

// Add this to test setup
options.FlushEventsImmediately = false;

Production Data Loss?

// Verify production config
options.FlushEventsImmediately = true; // ← Must be true!

Performance Issues?

• Check storage type (HDD vs SSD)
• Consider Phase 3 features (batch flushing, WAL)
• Monitor with metrics (future feature)

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For full details, see the implementation notes on GitHub.