MySqlCompressBlob1.cs

using System;
using MySql.Data.MySqlClient;

namespace MySqlCompressBlob
{
	class Program
	{
		static void Main(string[] args)
		{
			var csb = new MySqlConnectionStringBuilder
			{
				Server = "localhost",
				Database = "test",
				UserID = "root",
				Password = /* redacted */
				UseCompression = true,
			};

			using (var connection = new MySqlConnection(csb.ConnectionString))
			{
				connection.Open();

				using (var cmd = new MySqlCommand("drop table if exists test.blobs; create table test.blobs(data longblob)", connection))
					cmd.ExecuteNonQuery();

				var bytes = new byte[16519389]; // no exception with new byte[16519388]
				var random = new Random(1);
				random.NextBytes(bytes);

				using (var cmd = new MySqlCommand("insert into test.blobs(data) values(@data);", connection))
				{
					cmd.Parameters.AddWithValue("data", bytes);
					cmd.ExecuteNonQuery();
				}
			}
		}
	}
}