Preset Schemas

// Default — the 6-column schema shown above
var schema = DefaultSchema.Create("app_logs").Build();

// Minimal — just timestamp, level (numeric), and message
var schema = DefaultSchema.CreateMinimal("app_logs").Build();

// Comprehensive — default + full log event JSON
var schema = DefaultSchema.CreateComprehensive("app_logs").Build();

// Start from a preset and add custom columns
// Each preset returns a SchemaBuilder, which can be further customized before calling .Build()
var schema = DefaultSchema.Create("app_logs")
    .AddPropertyColumn("UserId", "Nullable(Int64)")
    .AddPropertyColumn("RequestPath", "Nullable(String)")
    .Build();

Custom Schema

Use the schema builder to control which columns are created, their names, types, and the table engine:

.WriteTo.ClickHouse(
    connectionString: "Host=localhost;Port=9000;Database=logs",
    configureSchema: schema => schema
        .WithTableName("custom_logs")
        .AddTimestampColumn("event_time", precision: 6)
        .AddLevelColumn("severity", asString: true)
        .AddMessageColumn()
        .AddExceptionColumn()
        .AddPropertiesColumn()
        .AddPropertyColumn("UserId", "Nullable(Int64)", writeMethod: PropertyWriteMethod.Raw)
        .AddPropertyColumn("RequestPath", "Nullable(String)")
        .WithEngine("ENGINE = MergeTree() ORDER BY (event_time) PARTITION BY toYYYYMM(event_time)"))

Schema Builder Methods

Choosing ORDER BY

ClickHouse query performance depends heavily on ORDER BY. For typical log tables:

// Good for time-range queries
.WithEngine("ENGINE = MergeTree() ORDER BY (timestamp)")

// Better if you often filter by level
.WithEngine("ENGINE = MergeTree() ORDER BY (level, timestamp)")

## Extracting Individual Properties

Use `SinglePropertyColumnWriter` to pull specific enriched properties into dedicated typed columns. This is useful when you want to query or index a known property efficiently instead of parsing JSON.

```csharp
.AddPropertyColumn("UserId", "Nullable(Int64)", writeMethod: PropertyWriteMethod.Raw)
.AddPropertyColumn("RequestPath", "Nullable(String)")
.AddPropertyColumn("CorrelationId", "Nullable(UUID)")

Write methods:

If a log event doesn't contain the named property, the sink sends a ClickHouse column default (the field is skipped and ClickHouse applies the type's default value, e.g. 0 for Int64, '' for String).

Table Creation Modes

.WriteTo.ClickHouse(
    connectionString: "...",
    tableName: "app_logs",
    tableCreation: TableCreationMode.CreateIfNotExists)  // default

Batching

The sink uses Serilog's BatchingOptions to control buffer size and flush events. You can tune the defaults:

.WriteTo.ClickHouse(
    connectionString: "Host=localhost;Port=9000;Database=logs",
    tableName: "app_logs",
    batchSizeLimit: 10_000,           // Max events per batch (default: 10,000)
    flushInterval: TimeSpan.FromSeconds(10),  // Time between flushes (default: 5s)
    queueLimit: 100_000)           // Max events in queue (default: 100,000)

Important:* Call Log.CloseAndFlush() on application shutdown to ensure buffered events are written. In ASP.NET Core, UseSerilog() handles this automatically.

Callbacks

Hook into batch lifecycle for metrics or alerting:

.WriteTo.ClickHouse(
    connectionString: "...",
    tableName: "app_logs",
    onBatchWritten: (count, duration) =>
        Console.WriteLine($"Wrote {count} events in {duration.TotalMilliseconds}ms"),
    onBatchFailed: (ex, count) =>
        Console.WriteLine($"Failed to write {count} events: {ex.Message}"))

Note that retries are handled by Serilog and controlled via RetryTimeLimit.

Full Options

For complete control, pass a ClickHouseSinkOptions directly:

var options = new ClickHouseSinkOptions
{
    ConnectionString = "Host=localhost;Port=9000;Database=logs",
    Schema = DefaultSchema.Create("app_logs").Build(),
    TableCreation = new TableCreationOptions
    {
        Mode = TableCreationMode.CreateIfNotExists,
        ValidateOnStartup = true
    },
    MinimumLevel = LogEventLevel.Information,
    FormatProvider = CultureInfo.InvariantCulture,
    OnBatchWritten = (count, duration) => { /* metrics */ },
    OnBatchFailed = (ex, count) => { /* alerting */ }
};

Log.Logger = new LoggerConfiguration()
    .WriteTo.ClickHouse(options)
    .CreateLogger();

Dependency Injection / ASP.NET

If you already have a ClickHouseClient or ClickHouseDataSource registered in your DI container, pass it directly instead of a connection string:

Using ClickHouseDataSource (.NET 7+)

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddSingleton(_ =>
    new ClickHouseDataSource("Host=localhost;Port=9000;Database=logs"));

builder.Host.UseSerilog((context, services, loggerConfiguration) =>
{
    var dataSource = services.GetRequiredService<ClickHouseDataSource>();
    loggerConfiguration.WriteTo.ClickHouse(dataSource, tableName: "app_logs");
});

Using ClickHouseClient

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddSingleton<IClickHouseClient>(_ =>
    new ClickHouseClient("Host=localhost;Port=8443;Protocol=https;Database=logs"));

builder.Host.UseSerilog((context, services, loggerConfiguration) =>
{
    var client = services.GetRequiredService<IClickHouseClient>();
    loggerConfiguration.WriteTo.ClickHouse(client, tableName: "app_logs");
});

All DI overloads accept the same optional parameters (database, batchSizeLimit, flushInterval, etc.) as the connection-string overload. For full control, pass a ClickHouseSinkOptions alongside the client or data source:

loggerConfiguration.WriteTo.ClickHouse(options, client);
loggerConfiguration.WriteTo.ClickHouse(options, dataSource); // .NET 7+

Connection String

The sink uses ClickHouse.Driver for the connection. Connection string format:

Host=localhost;Port=9000;Database=logs;User=default;Password=

Troubleshooting

See the serilog docs for debugging and diagnostics tips.

Supported Frameworks

net6.0, net8.0, net9.0, net10.0

License

Apache-2.0