ProxySQL and deprecated COM_PROCESS_KILL
Today we solved an issue where ProxySQL just asserts if it receives MySQL command which is not handled by ProxySQL. So, COM_PROCESS_KILL was an applicant. Here is the backtrace:
(gdb) bt
#0 0x00007f3601ee75f7 in raise () from /lib64/libc.so.6
#1 0x00007f3601ee8ce8 in abort () from /lib64/libc.so.6
#2 0x00007f3601ee0566 in __assert_fail_base () from /lib64/libc.so.6
#3 0x00007f3601ee0612 in __assert_fail () from /lib64/libc.so.6
#4 0x0000000000466242 in MySQL_Session::handler (this=this@entry=0x7f35f8631000) at MySQL_Session.cpp:1745
#5 0x0000000000454dc4 in MySQL_Thread::process_all_sessions (this=this@entry=0x7f35f860d000) at MySQL_Thread.cpp:2678
#6 0x000000000045cfd1 in MySQL_Thread::run (this=this@entry=0x7f35f860d000) at MySQL_Thread.cpp:2518
#7 0x0000000000438f24 in mysql_worker_thread_func (arg=0x7f360043c9b0) at main.cpp:165
#8 0x00007f3603712dc5 in start_thread () from /lib64/libpthread.so.0
#9 0x00007f3601fa8ced in clone () from /lib64/libc.so.6
(gdb) x/32b pkt->ptr
0x7fddcd819660: 5 0 0 0 12 -61 0 0
0x7fddcd819668: 0 0 0 0 4 0 0 0
0x7fddcd819670: -128 115 -81 -52 -35 127 0 0
0x7fddcd819678: 0 0 0 0 0 0 0 0
(gdb) p pkt
$4 = {ptr = 0x7fddcd819660, size = 9}
First bytes are mysql header, 12 is the mysql command, which in this case is https://dev.mysql.com/doc/internals/en/com-process-kill.html.
12 = 0x0c, so the first 4 bytes is a mysql header (5 0 0 0) that also specifies that the length of the payload is 5 bytes. 5 bytes payload + 4 bytes header = 9 bytes in total. So the first byte of the payload identifies the type of command.
This behavior by ProxySQL was fixed.