What are the common causes and solutions for high CPU usage of MySQL in cloud database?

Common Causes and Solutions for High CPU Usage of MySQL in Cloud Database

1. Inefficient Queries

Cause: Poorly optimized queries (e.g., missing indexes, full table scans) can cause excessive CPU load.
Solution:

• Use EXPLAIN to analyze query execution plans.
• Add missing indexes on frequently filtered or joined columns.
• Rewrite complex queries into simpler ones.

Example:

-- Before (full table scan)  
SELECT * FROM users WHERE email = 'test@example.com';  

-- After (with index)  
CREATE INDEX idx_email ON users(email);  
SELECT * FROM users WHERE email = 'test@example.com';  

Tencent Cloud Solution: Use TencentDB for MySQL's Slow Query Log and Database Audit features to identify and optimize problematic queries.

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2. High Concurrency or Connection Overhead

Cause: Too many concurrent connections or threads can exhaust CPU resources.
Solution:

• Increase max_connections cautiously (avoid over-allocation).
• Use connection pooling (e.g., ProxySQL or TencentDB for MySQL's built-in proxy).
• Limit idle connections with wait_timeout.

Example:

-- Reduce idle connections  
SET GLOBAL wait_timeout = 60;  

Tencent Cloud Solution: TencentDB for MySQL supports automatic connection scaling and read/write splitting to distribute workload efficiently.

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3. Lack of Indexes or Incorrect Index Usage

Cause: Missing or redundant indexes force MySQL to scan entire tables.
Solution:

• Use SHOW INDEX to check existing indexes.
• Optimize indexes for frequently queried columns.
• Avoid redundant indexes (e.g., (col1, col2) and (col1)).

Tencent Cloud Solution: TencentDB for MySQL provides Index Advisor to recommend optimal indexes.

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4. Insufficient Buffer Pool Size

Cause: Small innodb_buffer_pool_size leads to frequent disk I/O, increasing CPU usage.
Solution:

• Allocate more memory to innodb_buffer_pool_size (typically 70-80% of available RAM).
• Monitor buffer pool hit ratio (SHOW ENGINE INNODB STATUS).

Example:

-- Set buffer pool size (in my.cnf)  
innodb_buffer_pool_size = 4G;  

Tencent Cloud Solution: TencentDB for MySQL allows vertical scaling to increase memory and CPU resources dynamically.

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5. Background Processes (e.g., Purging, Replication)

Cause: Heavy background tasks (e.g., binary log purging, replication lag) consume CPU.
Solution:

• Adjust expire_logs_days to control binary log retention.
• Optimize replication settings (e.g., sync_binlog).

Tencent Cloud Solution: TencentDB for MySQL offers automated log management and high-availability replication to minimize overhead.

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6. Malware or Unauthorized Queries

Cause: Malicious queries (e.g., crypto-mining) can spike CPU usage.
Solution:

• Enable TencentDB for MySQL's security audit and IP whitelisting.
• Regularly monitor unusual query patterns.

Tencent Cloud Solution: TencentDB for MySQL includes built-in DDoS protection and intrusion detection to safeguard against attacks.

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By addressing these causes with proper optimization and leveraging TencentDB for MySQL's features, high CPU usage can be effectively mitigated.