'proxysql_mysql_backend/frontend_buffers_bytes' metrics don't report the actual values

[JavierJF]

• A clear description of the issue

Both metrics:

• proxysql_mysql_backend_buffers_bytes
• proxysql_mysql_frontend_buffers_bytes

Are not reporting the actual values being reported when issuing a query like:

mysql> select * from stats.stats_mysql_global where Variable_Name like '%buffer%';
+------------------------------+----------------+
| Variable_Name                | Variable_Value |
+------------------------------+----------------+
| mysql_backend_buffers_bytes  | 283616         |
| mysql_frontend_buffers_bytes | 262144         |
+------------------------------+----------------+
2 rows in set (0.01 sec)

# HELP proxysql_mysql_backend_buffers_bytes Buffers related to backend connections if "fast_forward" is used (0 means fast_forward is not used).
# TYPE proxysql_mysql_backend_buffers_bytes gauge
proxysql_mysql_backend_buffers_bytes 0.000000
# HELP proxysql_mysql_frontend_buffers_bytes Buffers related to frontend connections (read/write buffers and other queues).
# TYPE proxysql_mysql_frontend_buffers_bytes gauge
proxysql_mysql_frontend_buffers_bytes 0.000000

• ProxySQL version

• v2.x

• OS version

NAME="Arch Linux"
PRETTY_NAME="Arch Linux"
ID=arch
BUILD_ID=rolling

• The steps to reproduce the issue

1. Create some load for a ProxySQL instance:

sysbench --db-driver=mysql --mysql-user=__user__ --mysql_password=__pass__ --mysql-db=sysbench --mysql-host=127.0.0.1 --mysql-port=6033 --tables=10 --table-size=10000 --threads=4 --time=0 --events=0 --report-interval=1 --mysql-ignore-errors='all' oltp_read_write run

2. Check that the value reported by the following queries doesn't match:

• select * from stats.stats_mysql_global where Variable_Name like '%buffer%'
• SHOW PROMETHEUS METRICS