sv_diff returns zero rows

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What steps will reproduce the problem?
1. Set up mycheckpoint to monitor a live server remotely, as follows:
/etc/mycheckpoint.cnf:

[mycheckpoint]
#smtp_host = mail.my-server-company.com
#smtp_from = monitor@my-server-company.com
#smtp_to = dba@my-server-company.com
monitored_port=3306
monitored_host=livedbserver.com
monitored_user=monitoring_user
monitored_password=[*****]
purge_days = 60

[client]
user=monitoring_user
password=[*****]
socket=/var/run/mysqld/mysqld.sock
port=3306
host=localhost
database=mycheckpoint
skip_check_replication=True

2. Deploy and run:

user@monitoringhost$ mycheckpoint deploy
Add the following row to crontab:
*/5 * * * * mycheckpoint

What is the expected output? What do you see instead?

While mycheckpoint is logging rows into the status_variables table, I'm not 
getting any rows from the sv_diff view:

mysql> SELECT questions, uptime, warning_count, ts FROM status_variables;
+-----------+---------+---------------+---------------------+
| questions | uptime  | warning_count | ts                  |
+-----------+---------+---------------+---------------------+
| 241039414 | 1281504 |             0 | 2012-11-02 16:20:01 |
| 241101176 | 1281804 |             0 | 2012-11-02 16:25:01 |
| 241152461 | 1282105 |             0 | 2012-11-02 16:30:01 |
| 241205392 | 1282405 |             0 | 2012-11-02 16:35:01 |
| 241258591 | 1282705 |             0 | 2012-11-02 16:40:01 |
| 241307251 | 1283005 |             0 | 2012-11-02 16:45:02 |
| 241354124 | 1283305 |             0 | 2012-11-02 16:50:01 |
| 241409544 | 1283605 |             0 | 2012-11-02 16:55:01 |
| 241459330 | 1283905 |             0 | 2012-11-02 17:00:01 |
| 241501222 | 1284205 |             0 | 2012-11-02 17:05:01 |
+-----------+---------+---------------+---------------------+
10 rows in set (0.00 sec)

mysql> SELECT * FROM sv_diff;
Empty set (0.00 sec)

mysql>

What is the output when running with the "--verbose --debug" options?

user@monitoringhost$ mycheckpoint --verbose --debug
-- Using /etc/mycheckpoint.cnf as defaults file
-- mycheckpoint rev 208, build 201011041330. Copyright (c) 2009-2010 by Shlomi 
Noach
-- database is mycheckpoint
-- monitored host is: livedbserver.com
-- Global status & variables recorded
-- Non-local monitoring; will not read OS data
-- New entry added: id=22; ts=2012-11-02 17:08:32
-- Collecting custom data
-- No alert conditions defined
-- Status variables checkpoint complete


What version of the mycheckpoint are you using?
Revision 208

What version of the MySQL are you using? (SELECT VERSION())
livedbserver.com:
mysql> SELECT VERSION();
+----------------+
| VERSION()      |
+----------------+
| 5.1.65-ius-log |
+----------------+
1 row in set (0.00 sec)


Monitoring host:
mysql> SELECT VERSION();
+-----------------------------+
| VERSION()                   |
+-----------------------------+
| 5.1.61-0ubuntu0.10.10.1-log |
+-----------------------------+
1 row in set (0.00 sec)



What version of Python are you using? (python --version)

user@monitoringhost$ python --version
Python 2.6.6


On what operating system?
livedbserver.com:
CentOS

Monitoring host:
Ubuntu



What is your sql_mode? (SELECT @@global.sql_mode)
livedbserver.com:

mysql> SELECT @@global.sql_mode;
+-------------------+
| @@global.sql_mode |
+-------------------+
|                   |
+-------------------+
1 row in set (0.00 sec)

Monitoring host:

mysql> SELECT @@global.sql_mode;
+-------------------+
| @@global.sql_mode |
+-------------------+
|                   |
+-------------------+
1 row in set (0.00 sec)

Original issue reported on code.google.com by ale...@viovet.co.uk on 2 Nov 2012 at 5:16