Asynchronous Triggers in SQL Server 2005/2008

To perform asynchronous processing you can use Service Broker, but it isn't the only option, you can also use CLR objects.

The following is an example of an stored procedure (AsyncProcedure) that asynchronous calls another procedure (SyncProcedure):

using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.Runtime.Remoting.Messaging;
using System.Diagnostics;

public delegate void AsyncMethodCaller(string data, string server, string dbName);

public partial class StoredProcedures
{
    [Microsoft.SqlServer.Server.SqlProcedure]
    public static void AsyncProcedure(SqlXml data)
    {
        AsyncMethodCaller methodCaller = new AsyncMethodCaller(ExecuteAsync);
        string server = null;
        string dbName = null;
        using (SqlConnection cn = new SqlConnection("context connection=true"))
        using (SqlCommand cmd = new SqlCommand("SELECT @@SERVERNAME AS [Server], DB_NAME() AS DbName", cn))
        {
            cn.Open();
            using (SqlDataReader reader = cmd.ExecuteReader())
            {
                reader.Read();
                server = reader.GetString(0);
                dbName = reader.GetString(1);
            }
        }
        methodCaller.BeginInvoke(data.Value, server, dbName, new AsyncCallback(Callback), null);
        //methodCaller.BeginInvoke(data.Value, server, dbName, null, null);
    }

    private static void ExecuteAsync(string data, string server, string dbName)
    {
        string connectionString = string.Format("Data Source={0};Initial Catalog={1};Integrated Security=SSPI", server, dbName);
        using (SqlConnection cn = new SqlConnection(connectionString))
        using (SqlCommand cmd = new SqlCommand("SyncProcedure", cn))
        {
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.Add("@data", SqlDbType.Xml).Value = data;
            cn.Open();
            cmd.ExecuteNonQuery();
        }
    }

    private static void Callback(IAsyncResult ar)
    {
        AsyncResult result = (AsyncResult)ar;
        AsyncMethodCaller caller = (AsyncMethodCaller)result.AsyncDelegate;
        try
        {
            caller.EndInvoke(ar);
        }
        catch (Exception ex)
        {
            // handle the exception
            //Debug.WriteLine(ex.ToString());
        }
    }
}

It uses asynchronous delegates to call SyncProcedure:

CREATE PROCEDURE SyncProcedure(@data xml)
AS
  INSERT INTO T(Data) VALUES (@data)

Example of calling AsyncProcedure:

EXEC dbo.AsyncProcedure N'<doc><id>1</id></doc>'

Unfortunatelly, the assembly requires UNSAFE permission.

You can't make the trigger run asynchronously, but you could have the trigger synchronously send a message to a SQL Service Broker queue. The queue can then be processed asynchronously by a stored procedure.

these articles show how to use service broker for async auditing and should be useful:

Centralized Asynchronous Auditing with Service Broker

Service Broker goodies: Cross Server Many to One (One to Many) scenario and How to troubleshoot it

SQL Server 2014 introduced a very interesting feature called Delayed Durability. If you can tolerate loosing a few rows in case of an catastrophic event, like a server crash, you could really boost your performance in schenarios like yours.

Delayed transaction durability is accomplished using asynchronous log writes to disk. Transaction log records are kept in a buffer and written to disk when the buffer fills or a buffer flushing event takes place. Delayed transaction durability reduces both latency and contention within the system

The database containing the table must first be altered to allow delayed durability.

ALTER DATABASE dbname SET DELAYED_DURABILITY = ALLOWED

Then you could control the durability on a per-transaction basis.

begin tran

insert into ChangeTrackingTable select * from inserted

commit with(DELAYED_DURABILITY=ON)

The transaction will be commited as durable if the transaction is cross-database, so this will only work if your audit table is located in the same database as the trigger.

There is also a possibility to alter the database as forced instead of allowed. This causes all transactions in the database to become delayed durable.

ALTER DATABASE dbname SET DELAYED_DURABILITY = FORCED

For delayed durability, there is no difference between an unexpected shutdown and an expected shutdown/restart of SQL Server. Like catastrophic events, you should plan for data loss. In a planned shutdown/restart some transactions that have not been written to disk may first be saved to disk, but you should not plan on it. Plan as though a shutdown/restart, whether planned or unplanned, loses the data the same as a catastrophic event.

This strange defect will hopefully be addressed in a future release, but until then it may be wise to make sure to automatically execute the 'sp_flush_log' procedure when SQL server is restarting or shutting down.