troubleshoot high cpu from mysql on ubuntu

High CPU usage on a MySQL database server can have various causes. To identify and diagnose the issue, you should follow these steps:

1. Identify the Running Queries

You should first identify the running queries, particularly the ones that might be consuming high CPU. You can use the following command:

sql

SHOW FULL PROCESSLIST;

This will display a list of currently executing threads in MySQL. Look for queries that have been running for a long time or are using a lot of resources.

Alternatively, you can use:

sql

SHOW PROCESSLIST;

2. Analyze the Slow Query Log

The slow query log can help you identify queries that are taking a long time to execute. If the slow query log is not enabled, you can enable it by running:

sql

SET GLOBAL slow_query_log = 'ON';

Then, check the slow query log file to identify long-running queries:

bash

cat /var/log/mysql/mysql-slow.log

Note: The path to the log file might differ based on your setup.

3. Use Performance Schema

Performance Schema in MySQL provides insight into server performance. Start with the events_statements_history_long table to see the latest queries executed:

sql

SELECT *

FROM performance_schema.events_statements_history_long

ORDER BY timer_end DESC

LIMIT 10;

This will show the last 10 executed queries.

4. Optimize Queries

Once you've identified potential problematic queries, analyze their execution plans using EXPLAIN:

sql

EXPLAIN <your_query_here>;

This will provide insight into how MySQL is executing the query. Look for issues like full table scans or missing indexes.

5. Check System Metrics

Check system-level metrics to see if MySQL is constrained by CPU, memory, or I/O:

CPU: Use tools like top or htop to identify which process is consuming the most CPU.
Memory: Ensure that MySQL has sufficient memory allocated. Use free -h to check available memory.
I/O: Check disk I/O with iostat or vmstat.

6. Check MySQL Configuration

Misconfigured settings can lead to high CPU usage. Key settings to review include:

innodb_buffer_pool_size: Should be set to 60-80% of available memory.
query_cache_size: Should generally be set to 0 or off (OFF).
max_connections: Set according to the expected traffic.

7. Monitor and Tune

After making adjustments, monitor the server to see if CPU usage improves. Use monitoring tools like MySQL Workbench, Grafana, or Nagios to track server performance over time.

Conclusion

High CPU usage on a MySQL database can stem from a variety of causes, including inefficient queries, misconfigurations, or insufficient resources. By following these steps, you can diagnose and address the underlying issues.