A fix for Bug#22891 "session level max_allowed_packet can be

set but is ignored".
                                  
This patch makes @@session.max_allowed_packed and
@@session.net_buffer_length read-only as suggested in the bug
report. The user will have to use SET GLOBAL (and reconnect)
to alter the session values of these variables.
                            
The error string ER_VARIABLE_IS_READONLY is introduced.
                            
Tests are modified accordingly.


sql/set_var.cc:
  The class sys_var_thd_ulong_session_readonly is introduced as
  a specialization of sys_var_thd_ulong implementing a read-only
  session variable. The class overrides check() and
  check_default() to achieve the read-only property for the
  session part of the variable.
sql/set_var.h:
  The class sys_var_thd_ulong_session_readonly is introduced as
  a specialization of sys_var_thd_ulong implementing a read-only
  session variable. The class overrides check() and
  check_default() to achieve the read-only property for the
  session part of the variable.
sql/share/errmsg.txt:
  New error ER_VARIABLE_IS_READONLY.

1 files changed, 10 insertions, 12 deletions

diff --git a/mysql-test/t/variables.test b/mysql-test/t/variables.test
index 221f46605cd..e98436fa62c 100644
--- a/mysql-test/t/variables.test
+++ b/mysql-test/t/variables.test
@@ -146,25 +146,23 @@ show global variables like 'myisam_max_sort_file_size';
 --replace_result 9223372036853727232 FILE_SIZE 2146435072 FILE_SIZE
 select * from information_schema.global_variables where variable_name like 'myisam_max_sort_file_size';
 
+# bug#22891: modified to take read-only SESSION net_buffer_length into account
 set global net_retry_count=10, session net_retry_count=10;
 set global net_buffer_length=1024, net_write_timeout=200, net_read_timeout=300;
-set session net_buffer_length=2048, net_write_timeout=500, net_read_timeout=600;
 show global variables like 'net_%';
 select * from information_schema.global_variables where variable_name like 'net_%' order by 1;
 show session variables like 'net_%';
 select * from information_schema.session_variables where variable_name like 'net_%' order by 1;
-set session net_buffer_length=8000, global net_read_timeout=900, net_write_timeout=1000;
+set global net_buffer_length=8000, global net_read_timeout=900, net_write_timeout=1000;
 show global variables like 'net_%';
 select * from information_schema.global_variables where variable_name like 'net_%' order by 1;
-show session variables like 'net_%';
-select * from information_schema.session_variables where variable_name like 'net_%' order by 1;
-set net_buffer_length=1;
-show variables like 'net_buffer_length';
-select * from information_schema.session_variables where variable_name like 'net_buffer_length';
+set global net_buffer_length=1;
+show global variables like 'net_buffer_length';
+select * from information_schema.global_variables where variable_name like 'net_buffer_length';
 #warning 1292
-set net_buffer_length=2000000000;
-show variables like 'net_buffer_length';
-select * from information_schema.session_variables where variable_name like 'net_buffer_length';
+set global net_buffer_length=2000000000;
+show global variables like 'net_buffer_length';
+select * from information_schema.global_variables where variable_name like 'net_buffer_length';
 
 set character set cp1251_koi8;
 show variables like "character_set_client";
@@ -274,7 +272,7 @@ select @@long_query_time;
 set long_query_time=100.000001;
 select @@long_query_time;
 set low_priority_updates=1;
-set max_allowed_packet=100;
+set global max_allowed_packet=100;
 set global max_binlog_cache_size=100;
 set global max_binlog_size=100;
 set global max_connect_errors=100;
@@ -288,7 +286,7 @@ set global max_user_connections=100;
 select @@max_user_connections;
 set global max_write_lock_count=100;
 set myisam_sort_buffer_size=100;
-set net_buffer_length=100;
+set global net_buffer_length=100;
 set net_read_timeout=100;
 set net_write_timeout=100;
 set global query_cache_limit=100;