Monitoring The Active Connections In MySQL

Each client that communicates with a MySQL server establishes a separate connection. Monitoring and analyzing these connections is crucial for database performance tuning, capacity planning, and ensuring the server isn’t overwhelmed with too many connections.

How to Monitor Connection Count in MySQL:

1. Show Current Connections:
   Use the SHOW STATUS Command to view the current number of active connections:

   SHOW STATUS LIKE 'Threads_connected';

2. Show Maximum Connections Ever Reached:
   To see the highest number of simultaneous connections since the server started:

   SHOW STATUS LIKE 'Max_used_connections';

3. Show Configured Maximum Allowed Connections:
   The max_connections Variable sets the maximum permitted number of simultaneous client connections. By default, this is 151. Check its value with:

   SHOW VARIABLES LIKE 'max_connections';

Analyzing the Connection Count:

1. High Connection Count: If the number of active connections (Threads_connected) is frequently near the max_connections limit, it suggests that you might need to increase the max_connections Setting. However, before doing so, it’s essential to ensure that the server’s hardware, especially memory, can handle the increased number of connections.
2. Connection Errors: If clients are frequently getting “Too many connections” errors, it’s a clear sign that the max_connections limit is being reached and needs reevaluation.
3. Connection Usage: Comparing Threads_connected with Max_used_connections can give an idea about connection usage patterns. If Max_used_connections it is significantly high, it means there was a point when many clients were connected simultaneously.
4. Historical Analysis with mysqladmin:
   The mysqladmin tool can provide status variables at regular intervals. This is useful for tracking connection patterns:

   mysqladmin -u root -p -i 5 extended-status | grep "Threads_connected"

This command will show the Threads_connected status every 5 seconds, allowing you to monitor connection count in real-time.

5. Check Aborted Connections:
   If you see a high count of aborted connections, it may indicate that clients are connecting and disconnecting too often, possibly due to network issues or incorrect credentials:

   SHOW STATUS LIKE 'Aborted_connects';

6. Performance Schema: MySQL’s Performance Schema provides detailed insights into server execution at a low level. By querying relevant tables in the performance schema, you can get a deeper understanding of connection attributes, events, and potential bottlenecks.

Tips:

• Always monitor the system’s performance when increasing the max_connections value. More connections might lead to more RAM usage, and the system could run out of memory, causing other issues.
• Consider using connection pooling solutions like ProxySQL or MySQL Router to maintain and reuse connections more efficiently, especially for applications that frequently open and close connections.
• Regularly monitor slow queries, as a small number of poorly optimized queries can impact performance more than a large number of connections executing optimized queries.

Remember, while the connection count is a vital metric, it’s just one of many aspects you should monitor to ensure the optimal performance of your MySQL server.