Serilog.Sinks.Async

An asynchronous wrapper for other Serilog sinks. Use this sink to reduce the overhead of logging calls by delegating work to a background thread. This is especially suited to non-batching sinks like the File and RollingFile sinks that may be affected by I/O bottlenecks.
Note: many of the network-based sinks (CouchDB, Elasticsearch, MongoDB, Seq, Splunk...) already perform asynchronous batching natively and do not benefit from this wrapper.
Getting started
Install from NuGet:
dotnet add package Serilog.Sinks.Async
Assuming you have already installed the target sink, such as the file sink, move the wrapped sink's configuration within a WriteTo.Async()
statement:
Log.Logger = new LoggerConfiguration()
.WriteTo.Async(a => a.File("logs/myapp.log"))
.CreateLogger()
Log.Information("This will be written to disk on the worker thread");
Log.CloseAndFlush();
The wrapped sink (File
in this case) will be invoked on a worker thread while your application's thread gets on with more important stuff.
Because the memory buffer may contain events that have not yet been written to the target sink, it is important to call Log.CloseAndFlush()
or Logger.Dispose()
when the application exits.
Buffering & Dropping
The default memory buffer feeding the worker thread is capped to 10,000 items, after which arriving events will be dropped. To increase or decrease this limit, specify it when configuring the async sink. One can determine whether events have been dropped via Serilog.Async.IAsyncLogEventSinkInspector.DroppedMessagesCount
(see Sink State Inspection interface below).
.WriteTo.Async(a => a.File("logs/myapp.log"), bufferSize: 500)
Health Monitoring via the Monitor and Inspector interfaces
The Async
wrapper is primarily intended to allow one to achieve minimal logging latency at all times, even when writing to sinks that may momentarily block during the course of their processing (e.g., a File
Sink might block for a low number of ms while flushing). The dropping behavior is an important failsafe; it avoids having an unbounded buffering behaviour should logging throughput overwhelm the sink, or the sink ingestion throughput degrade.
In practice, this configuration (assuming one provisions an adequate bufferSize
) achieves an efficient and resilient logging configuration that can safely handle load without impacting processing throughput. The risk is of course that events get be dropped if the buffer threshold gets breached. The inspection interface, IAsyncLogEventSinkInspector
(obtained by providing an IAsyncLogEventSinkMonitor
when configuring the Async
Sink), enables a health monitoring mechanism to actively validate that the buffer allocation is not being exceeded in practice.
void ExecuteAsyncBufferCheck(IAsyncLogEventSinkInspector inspector)
{
var usagePct = inspector.Count * 100 / inspector.BufferSize;
if (usagePct > 50) SelfLog.WriteLine("Log buffer exceeded {0:p0} usage (limit: {1})", usagePct, inspector.BufferSize);
}
class MonitorConfiguration : IAsyncLogEventSinkMonitor
{
public void StartMonitoring(IAsyncLogEventSinkInspector inspector) =>
HealthMonitor.AddPeriodicCheck(() => ExecuteAsyncBufferCheck(inspector));
public void StopMonitoring(IAsyncLogEventSinkInspector inspector)
{ }
}
var monitor = new MonitorConfiguration();
.WriteTo.Async(a => a.File("logs/myapp.log"), monitor: monitor) ...
Blocking
Warning: For the same reason one typically does not want exceptions from logging to leak into the execution path, one typically does not want a logger to be able to have the side-effect of actually interrupting application processing until the log propagation has been unblocked.
When the buffer size limit is reached, the default behavior is to drop any further attempted writes until the queue abates, reporting each such failure to the Serilog.Debugging.SelfLog
. To replace this with a blocking behaviour, set blockWhenFull
to true
.
.WriteTo.Async(a => a.File("logs/myapp.log"), blockWhenFull: true)
XML <appSettings>
and JSON configuration
Using Serilog.Settings.Configuration JSON:
{
"Serilog": {
"WriteTo": [{
"Name": "Async",
"Args": {
"configure": [{
"Name": "Console"
}]
}
}]
}
}
XML configuration support has not yet been added for this wrapper.
About this sink
This sink was created following this conversation thread: https://github.com/serilog/serilog/issues/809.