MySQL High CPU/Memory Usage
- Identify slow queries using the slow query log:
- Enable the slow query log if it's not already enabled:SET GLOBAL slowquerylog = 'ON';
SET GLOBAL longquerytime = 2; -- Adjust based on need, captures queries taking longer than 2 seconds.
SET GLOBAL slowquerylog_file = '/path/to/your/logfile.log';
- Analyze the log file using tools like `mysqldumpslow` or `pt-query-digest` to find the most resource-intensive queries.
- Use the `SHOW PROCESSLIST;` command to identify currently running queries that could be causing high load.
- Examine specific session or query performance with the `SHOW FULL PROCESSLIST;` command to get more details on what each thread is executing.
- Analyze table sizes and row counts that can impact performance:
SELECT tableschema AS `Database`, tablename AS `Table`,
round(((datalength + indexlength) / 1024 / 1024), 2) `Size in MB`
FROM information_schema.TABLES
ORDER BY (datalength + indexlength) DESC;
- Check for missing indexes:
- Use the `EXPLAIN` statement on slow queries to check if indexes are being used effectively.
- Investigate columns used in JOIN, WHERE, ORDER BY, and GROUP BY clauses for potential indexing.
- Check memory and buffer usage:
- Query performance schema or information_schema to analyze memory allocation:SELECT * FROM sys.x$memoryglobalbycurrentbytes WHERE currentcount > 0 ORDER BY currentallocated DESC;
- Adjust key buffer sizes if necessary, for example:SET GLOBAL keybuffersize = 268435456; -- Adjust size according to analysis
- Reduce persistent connections or optimize DB connections settings if too many connections are causing high memory usage:
- Check max connections:SHOW VARIABLES LIKE "max_connections";
- Adjust if necessary:SET GLOBAL max_connections = 200; -- Adjust based on your server’s capability and needs.
- If InnoDB engine is used, analyze and adjust InnoDB buffer pool size:
- Check current buffer pool size:SHOW VARIABLES LIKE 'innodbbufferpool_size';
- Adjust the buffer pool size (example):SET GLOBAL innodbbufferpool_size = 134217728; -- Adjust based on system RAM and MySQL documentation.
- Optimize or repair tables if there are signs of table corruption or fragmentation, especially for MyISAM tables:
OPTIMIZE TABLE yourtablename;
10. Finally, if specific queries are identified as problematic, consider rewriting them for efficiency or implementing caching mechanisms to reduce database load.
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