COM_STMT_FETCH - RECEIVED AN UNKNOWN COMMAND: 28

[eminugurkenar]

proxysql-1.3.3-1
MysQL percona 5.7.10-3 (master-slave)

Hi,

We appreciate this tool.
We tried to switch master database via proxysql. While switching there was no request to proxysql (entering maintenance mode on web servers). We stop the replication on slave server then executed commands below on proxysql.

delete from mysql_servers where hostname='master';
update mysql_servers set hostgroup_id=0 where hostname='slave';
load mysql servers to runtime;
save mysql servers to disk;

After executed this commands we tested the connection and everything was working as expected. Then we exit maintenance mode. After a while (about 1 minutes later) we got too many connection on web servers. (proxsql status_client_connections_connected was 2048 which is max.)

We got the "PLEASE REPORT A BUG" on proxysql logs.
After restarting proxysql the problem has gone and everthing works as before.

Thank you.

Logs while we are getting too many connection.

2017-01-25 11:05:53 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:05:54 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:05:54 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:05:55 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:05:55 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:05:55 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:05:57 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:05:57 MySQL_Session.cpp:2253:handler(): [WARNING] Error during query on (0,,3306): 1062, Duplicate entry '36387494-174' for key 'PRIMARY'
2017-01-25 11:05:58 MySQL_Session.cpp:2253:handler(): [WARNING] Error during query on (0,,3306): 1062, Duplicate entry '0-0' for key 'PRIMARY'
2017-01-25 11:05:58 MySQL_Session.cpp:2253:handler(): [WARNING] Error during query on (0,,3306): 1062, Duplicate entry '0-0' for key 'PRIMARY'
2017-01-25 11:05:58 MySQL_Session.cpp:2253:handler(): [WARNING] Error during query on (0,,3306): 1062, Duplicate entry '0-0' for key 'PRIMARY'
2017-01-25 11:05:58 MySQL_Session.cpp:2253:handler(): [WARNING] Error during query on (0,,3306): 1062, Duplicate entry '0-0' for key 'PRIMARY'
2017-01-25 11:05:59 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:00 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:00 MySQL_Session.cpp:2253:handler(): [WARNING] Error during query on #(0,3306): 1062, Duplicate entry '0-0' for key 'PRIMARY'
2017-01-25 11:06:00 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:00 MySQL_Session.cpp:2253:handler(): [WARNING] Error during query on (0,,3306): 1062, Duplicate entry '0-0' for key 'PRIMARY'
2017-01-25 11:06:01 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:01 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:01 MySQL_Session.cpp:2253:handler(): [WARNING] Error during query on (0,,3306): 1062, Duplicate entry '0-0' for key 'PRIMARY'
2017-01-25 11:06:01 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:02 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:03 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:03 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:04 MySQL_Session.cpp:2253:handler(): [WARNING] Error during query on (0,,3306): 1062, Duplicate entry '0-0' for key 'PRIMARY'
2017-01-25 11:06:04 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:05 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
2017-01-25 11:06:05 MySQL_Session.cpp:1798:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG

[renecannao]

Hi, and thank you very much for the feedback and report.
Command 28 (0x1c) is COM_STMT_FETCH .
From the documentation on the same page, COM_STMT_FETCH:

Fetch rows from a existing resultset after a COM_STMT_EXECUTE

To me this is confusing, as after a COM_STMT_EXECUTE it should follow a COM_STMT_EXECUTE Response.
I surely need to study the protocol more. Maybe this is triggered when calling a stored procedure from a prepared statement.

Do you know which queries failed on the clients? This may help in creating some correlation.
Thanks.

[eminugurkenar]

Hi,
Sorry we don't know queries.