Bug #83329 MySqlException "Unknown command" inserting large blob with UseCompression=true
Submitted: 11 Oct 2016 4:37 Modified: 12 Oct 2016 9:41
Reporter: Bradley Grainger (OCA) Email Updates:
Status: Verified Impact on me:
Category:Connector / NET Severity:S2 (Serious)
Version:6.9.9, 7.0.5 OS:Windows (Windows 10 x64)
Assigned to: CPU Architecture:Any

[11 Oct 2016 4:37] Bradley Grainger
Windows 10 x64
Microsoft .NET Framework 4.6.2
Visual Studio 2015
MySql.Data 6.9.9

When MySqlConnectionStringBuilder.UseCompression = true is set, inserting a large random blob will throw the following exception:

Unhandled Exception: MySql.Data.MySqlClient.MySqlException: Unknown command
   at MySql.Data.MySqlClient.MySqlStream.ReadPacket()
   at MySql.Data.MySqlClient.NativeDriver.GetResult(Int32& affectedRow, Int64& insertedId)
   at MySql.Data.MySqlClient.Driver.NextResult(Int32 statementId, Boolean force)
   at MySql.Data.MySqlClient.MySqlDataReader.NextResult()
   at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(CommandBehavior behavior)
   at MySql.Data.MySqlClient.MySqlCommand.ExecuteNonQuery()
   at MySqlCompressBlob.Program.Main(String[] args) in Program.cs:line 33

I've pasted code to reproduce this at https://gist.github.com/bgrainger/ef06cf4d784a0df414f1a9406c74ccd8

In the example, creating a random blob of length 16519388 doesn't reproduce the problem, but making it one byte larger will.

Setting UseCompression=false will also work around the problem.

How to repeat:
Create a new C# console application with the source code at: https://gist.github.com/bgrainger/ef06cf4d784a0df414f1a9406c74ccd8

I've also reproduced the source below:

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))

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

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

				using (var cmd = new MySqlCommand("insert into test.blobs(data) values(@data);", connection))
					cmd.Parameters.AddWithValue("data", bytes);
[11 Oct 2016 4:43] Bradley Grainger
MySQL Server mysqld 5.7.11-log (on Windows 10 x64)
[11 Oct 2016 4:57] Bradley Grainger
Edit: fixed title s/blog/blob/
[12 Oct 2016 9:41] Chiranjeevi Battula
Hello Bradley Grainger,

Thank you for the bug report and test case.
Verified this behavior on Visual Studio 2013 (C#.Net) and Connector/NET 6.9.9 version.

[12 Oct 2016 9:41] Chiranjeevi Battula

Attachment: 83329.JPG (image/jpeg, text), 200.64 KiB.

[7 Apr 2020 16:13] Daniel Valdez
Posted by developer:
This test was done using all the specified versions and the mentioned error
didn't came up,
instead of that, we received the exception:
MySql.Data.MySqlClient.MySqlException: 'Packets larger than
max_allowed_packet are not allowed.'
Which is properly triggered, only when we modify the value of the variable
max_allowed_packet to be higher than the value to be inserted the test works
fine, the blob value is properly inserted in the database.