SET @@tx_isolation=X behaves like SET TRANSACATION ISOLATION LEVEL X instead of SET SESSSION tx_isolation=X

Thread 31 "mariadbd" hit Breakpoint 3, Sys_var_tx_isolation::session_update (this=0x17afc18 <Sys_tx_isolation>, thd=0x7f6a28000c58, var=0x7f6a280128c0)

    at /home/dan/repos/mariadb-server-10.4/sql/sys_vars.inl:2231

2231	    if (var->type == OPT_SESSION && Sys_var_enum::session_update(thd, var))

(gdb) p *var

$5 = (set_var) {<set_var_base> = {<Sql_alloc> = {<No data fields>}, _vptr$set_var_base = 0xf46d50 <vtable for set_var+16>}, var = 0x17afc18 <Sys_tx_isolation>, value = 0x7f6a28012830, type = SHOW_OPT_DEFAULT, 

  save_result = {ulonglong_value = 1, longlong_value = 1, double_value = 4.9406564584124654e-324, plugin = 0x1, plugins = 0x1, time_zone = 0x1, string_value = {

      str = 0x1 <error: Cannot access memory at address 0x1>, length = 140093914425568}, timestamp = {unix_time = 1, second_part = 140093914425568}, ptr = 0x1}, base = {str = 0x0, length = 0}}

Thread 31 "mariadbd" hit Breakpoint 3, Sys_var_tx_isolation::session_update (this=0x17afc18 <Sys_tx_isolation>, thd=0x7f6a28000c58, var=0x7f6a280128f8)

    at /home/dan/repos/mariadb-server-10.4/sql/sys_vars.inl:2231

2231	    if (var->type == OPT_SESSION && Sys_var_enum::session_update(thd, var))

(gdb) p *var

$4 = (set_var) {<set_var_base> = {<Sql_alloc> = {<No data fields>}, _vptr$set_var_base = 0xf46d50 <vtable for set_var+16>}, var = 0x17afc18 <Sys_tx_isolation>, value = 0x7f6a28012840, type = SHOW_OPT_SESSION, 

  save_result = {ulonglong_value = 2, longlong_value = 2, double_value = 9.8813129168249309e-324, plugin = 0x2, plugins = 0x2, time_zone = 0x2, string_value = {

      str = 0x2 <error: Cannot access memory at address 0x2>, length = 140093914425624}, timestamp = {unix_time = 2, second_part = 140093914425624}, ptr = 0x2}, base = {str = 0x0, length = 0}}

Thread 31 "mariadbd" hit Breakpoint 3, Sys_var_tx_isolation::session_update (this=0x17afc18 <Sys_tx_isolation>, thd=0x7f6a28000c58, var=0x7f6a280128f8)

    at /home/dan/repos/mariadb-server-10.4/sql/sys_vars.inl:2231

2231	    if (var->type == OPT_SESSION && Sys_var_enum::session_update(thd, var))

(gdb) p *var

$6 = (set_var) {<set_var_base> = {<Sql_alloc> = {<No data fields>}, _vptr$set_var_base = 0xf46d50 <vtable for set_var+16>}, var = 0x17afc18 <Sys_tx_isolation>, value = 0x7f6a28012838, type = SHOW_OPT_DEFAULT, 

  save_result = {ulonglong_value = 0, longlong_value = 0, double_value = 0, plugin = 0x0, plugins = 0x0, time_zone = 0x0, string_value = {str = 0x0, length = 140093914425624}, timestamp = {unix_time = 0, 

      second_part = 140093914425624}, ptr = 0x0}, base = {str = 0x0, length = 0}}