gistfile1.txt

private static void CopyFast()
{
    Stopwatch sw = new Stopwatch();            
    sw.Start();
    Task[] tasks = new Task[totalSegments];
    for (int segment = 0; segment < totalSegments; segment++)
    {
        int tmpSegment = segment;
        tasks[segment] = Task.Run(() => ScanSegment(tmpSegment));
    }
    
    Task.WaitAll(tasks);
    sw.Stop();

    Console.WriteLine($"Copy fast - {sw.ElapsedMilliseconds} milliseconds elapsed");
    Console.ReadLine();
}
private static async Task ScanSegment(int tmpSegment)
{
    var request = new ScanRequest
    {
        TableName = sourceTableName,
        Segment = tmpSegment,
        TotalSegments = totalSegments,
    };

    var result = await client.ScanAsync(request);

    for (var i = 0; i < result.Items.Count; i += 25)
    {
        var items = result.Items.Skip(i).Take(25).ToArray();
        var req = new BatchWriteItemRequest
        {
            RequestItems = new Dictionary<string, List<WriteRequest>>
            {
                {
                    destinationTableNameFast,
                    items.Select(i => new WriteRequest(new PutRequest(i))).ToList()
                }
            }
        };

        await client.BatchWriteItemAsync(req);
    }
}