Error
Error Code:
2055
MySQL Error 2055: Lost Connection to Server
Description
This error indicates that the client application unexpectedly lost its active connection to the MySQL server. It often occurs during a query execution or when the server terminates the connection due to various underlying issues, preventing further communication.
Error Message
Lost connection to MySQL server at '%s', system error: %d
Known Causes
4 known causesMySQL Server Instability or Shutdown
The MySQL server process may have crashed, been stopped, or restarted unexpectedly, leading to the immediate termination of all active client connections.
Network Connectivity Issues
Problems with the network infrastructure, such as firewall blocks, routing failures, or unstable internet connections, can interrupt the communication path between client and server.
Server Resource Exhaustion
The MySQL server might have run out of memory, reached its maximum allowed connections, or faced other resource limitations, causing it to drop client connections.
Long-Running Queries or Timeouts
Queries that take an excessively long time to execute may hit server-side or client-side timeout limits, leading the server to forcibly close the connection.
Solutions
4 solutions available1. Check Network Connectivity and Firewall Rules easy
Verify that the client can reach the MySQL server over the network and that no firewalls are blocking the connection.
1
From the client machine, ping the MySQL server's IP address or hostname to confirm basic network reachability.
ping your_mysql_server_ip_or_hostname2
Use telnet to test if the MySQL port (default 3306) is open and accessible from the client to the server.
telnet your_mysql_server_ip_or_hostname 33063
If telnet fails, check firewall rules on both the client and server. Ensure that the MySQL port (3306) is allowed for inbound traffic on the server and outbound traffic on the client.
4
On Linux/Unix servers, `iptables` or `firewalld` are common tools. On Windows, check Windows Firewall. Cloud environments often have their own security groups or network ACLs.
2. Increase MySQL Server Timeout Settings medium
Adjust MySQL server configuration variables that control connection timeouts to prevent premature disconnections.
1
Locate your MySQL configuration file (e.g., `my.cnf` or `my.ini`). The location varies by operating system and installation method.
2
Edit the configuration file to increase `wait_timeout` and `interactive_timeout`. These settings control how long the server waits for activity on a connection before closing it.
[mysqld]
wait_timeout = 28800
interactive_timeout = 288003
Restart the MySQL server service for the changes to take effect.
sudo systemctl restart mysql4
Alternatively, you can set these variables dynamically for the current session if you have sufficient privileges, though this is not a persistent solution.
SET GLOBAL wait_timeout = 28800;
SET GLOBAL interactive_timeout = 28800;3. Optimize Long-Running Queries and Server Load advanced
Address issues with slow or resource-intensive queries that might be causing the server to become unresponsive or drop connections.
1
Enable the MySQL slow query log to identify queries that are taking too long to execute.
[mysqld]
log_slow_queries = /var/log/mysql/mysql-slow.log
long_query_time = 22
Analyze the slow query log to identify problematic queries. Use tools like `mysqldumpslow` to summarize the log.
mysqldumpslow /var/log/mysql/mysql-slow.log3
Optimize identified slow queries by adding appropriate indexes, rewriting the query logic, or denormalizing tables if necessary.
CREATE INDEX index_name ON table_name (column_name);4
Monitor server resource utilization (CPU, memory, disk I/O). High resource usage can lead to performance degradation and connection drops. Consider upgrading hardware or optimizing the database schema and queries.
4. Verify MySQL Server Health and Resource Availability medium
Ensure the MySQL server process is running correctly and has sufficient system resources available.
1
Check if the MySQL server process is running on the server.
sudo systemctl status mysql2
If the service is not running, try starting it and check the MySQL error logs for clues about why it stopped.
sudo systemctl start mysql3
Examine the MySQL error log file (location varies, often in `/var/log/mysql/error.log` or within the data directory) for any critical errors or warnings that might indicate underlying problems.
4
Monitor system resources (CPU, RAM, disk space) on the MySQL server. Insufficient resources can cause the server to become unstable and drop connections.
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