Connection

The MariaDB Connection ID exists since long ago. So why bother about the Connection ID? Because it is interesting and you can do some interesting things with the Connection ID like tracking statements in your connections and find where they come from your application code.

The MariaDB Connection ID is a strictly monotonic increasing number starting with 1 at server restart:

shell> mariadb --user=root --execute='SELECT CONNECTION_ID()<br>G' | grep CONNECTION_ID
CONNECTION_ID(): 2372
shell> …

The General Query Log in MariaDB is a Log (file or table) that logs every statement sent from the Application to the MariaDB Database Server from the Connect Command to the Quit Command. A simple example you can find here:

bin/mysqld, Version: 10.4.6-MariaDB-log (MariaDB Server). started with:
Tcp port: 3306  Unix socket: /var/run/mysqld/mysql.sock
Time                Id Command  Argument
190709 21:27:30   3872 Connect  root@localhost as anonymous on test
                  3872 Query    INSERT INTO test …

How many connections can be opened concurrently against my MySQL or MariaDB database can be configured and checked with the following command:

SHOW GLOBAL VARIABLES LIKE 'max_connections';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_connections | 505   |
+-----------------+-------+

If this limit was ever reached in the past can be checked with:

SHOW GLOBAL STATUS LIKE 'max_use%';
+----------------------+-------+
| Variable_name        | Value | …

We recently run into some troubles with max_allowed_packet size problems during backups with the FromDual Backup/Recovery Manager and thus I investigated a bit more in the symptoms of such problems.

Read more about: max_allowed_packet.

A general rule for max_allowed_packet size to avoid problems is: All clients and the server should have set the same value for max_allowed_packet size!

I prepared some data for the test which looked as follows:

mysql> SELECT id, LEFT(data, 30), LENGTH(data), ts FROM test; …