MySQL High CPU/Memory Usage

The MySQL server consuming excessive CPU or memory resources, leading to system performance degradation.
  1. 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 long
querytime = 2; -- Adjust based on need, captures queries taking longer than 2 seconds.
SET GLOBAL slow
querylog_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.

  1. Use the `SHOW PROCESSLIST;` command to identify currently running queries that could be causing high load.



  1. Examine specific session or query performance with the `SHOW FULL PROCESSLIST;` command to get more details on what each thread is executing.



  1. Analyze table sizes and row counts that can impact performance:


SELECT tableschema AS `Database`, tablename AS `Table`,
round(((data
length + indexlength) / 1024 / 1024), 2) `Size in MB`
FROM information_schema.TABLES
ORDER BY (data
length + indexlength) DESC;

  1. 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.

  1. 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

  1. 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.

  1. 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.

  1. 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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