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In PHP, mysqli::debug is a powerful debugging tool that outputs detailed log information, helping developers analyze issues in the MySQL database connection and execution process. When developers encounter connection issues or queries that don't behave as expected while using the mysqli extension for database operations, the logs provided by mysqli::debug serve as a strong tool for troubleshooting.
mysqli::debug is a static method of the mysqli class that outputs debugging information to help developers view the interaction between the MySQL client and the database server. This information not only shows the details of SQL query execution but also includes the underlying connection status and error logs, greatly improving the efficiency of troubleshooting.
When you call mysqli::debug(), it will output a series of information, typically containing the following:
Connection Information:
It outputs the connection establishment process, including details such as the host, port, and more.
If the connection is successful, it will display a successful connection log; if it fails, it will show the error message.
Query Execution Information:
It outputs the execution details of each SQL query, including the raw query sent to the MySQL server, execution status, and error information (if any).
It includes the query execution time and whether the query was successful or failed.
Error Information:
If an error occurs during the connection or query execution process, mysqli::debug will record the error code and error message.
This is very helpful for diagnosing issues such as SQL syntax errors, permission problems, or connection interruptions.
Connection Close Information:
Once the database connection is closed, the debug log will record the event, ensuring that developers can clearly see the lifecycle of each connection.
Assume you call mysqli::debug() in your PHP code as follows:
mysqli::debug("m66.net");
The log output might look like this:
mysqli::debug ( MySQL debug output ):
MySQL debug output:
Host: m66.net Port: 3306
Connection id: 12345678
Connection established.
Query: SELECT * FROM users WHERE id = 1
Query sent to server: SELECT * FROM users WHERE id = 1
Query executed in 0.0023 seconds
Query result: Success
Query return: 1 row(s) retrieved
Connection closed.
Diagnosing Connection Issues:
If the database connection fails, mysqli::debug output will tell you the host and port used during the connection attempt, and whether the connection was successful. By reviewing this information, you can confirm whether the network or database configuration is correct.
Checking SQL Query Execution:
If a query does not execute as expected, the debug log provides the raw SQL query and its execution time, helping developers identify if the problem lies within the SQL statement itself. This is especially useful for complex queries, where the log can clearly show the execution process.
Identifying the Cause of Errors:
Error information is an important part of mysqli::debug output. If an error occurs during query execution (such as a syntax error, insufficient permissions, etc.), the log will provide the error code and message, helping developers quickly pinpoint the problem.
Analyzing Performance Bottlenecks:
By reviewing the query execution time in the logs, developers can identify queries that take longer to execute, and further analyze whether SQL statements or database structures need optimization.
mysqli::debug is a powerful tool for debugging MySQL database connection issues. By reviewing the logs it generates, developers can gain clear insights into the connection status, the execution details of SQL queries, and any errors that occur, enabling them to quickly identify and resolve problems. Understanding the content and format of these logs significantly improves debugging efficiency, especially when dealing with complex queries and database performance optimization. The information provided by mysqli::debug is invaluable in these scenarios.
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