Issue with Low Memory Usage on Azure MySQL Database

Question

I have been using Azure for hosting 5 systems/websites of my company for the past 4 years. Specifically, we have 5 Web App Services and 5 Azure Databases for MySQL.

Currently, I am experiencing an issue with the memory usage of one of the MySQL databases. The database is running on the B2s plan (2-core CPU and 4 GB memory). It consistently uses approximately 37% of the total memory (see attached image).

I have researched and attempted to adjust some parameters, but the memory usage remains unchanged.

Additionally, I would like to note that the website using this database has relatively high user activity/traffic compared to the other web apps. However, the memory usage of this database is always at a minimum, which seems counterintuitive.

This behavior seems unusual because, typically, I would expect issues like memory shortages or overflows, but not a stable yet seemingly low memory usage like this.

Has anyone encountered a similar issue? Any insights or suggestions would be greatly appreciated.

Answer 1

Hi ,

Thanks for reaching out to Microsoft Q&A.

The consistently low memory usage of your azure MySQL db despite high traffic might not necessarily indicate an issue. Here are some possible explanations and recommendations:

Possible Causes:

1. Efficient Query Optimization:
   • If your database queries are optimized, it’s possible they are not consuming much memory, even under high traffic. Indexing, proper use of joins, and avoiding unnecessary data retrieval can lead to efficient memory usage.
   Connection Management:
   • The memory footprint could remain low if connections to the database are being reused efficiently (connection pooling) rather than creating new connections for every query.
   Buffer Pool Configuration:

     - The `innodb_buffer_pool_size` parameter determines how much memory is allocated for caching data and indexes. A smaller buffer pool size might result in lower memory usage but could impact performance if the working dataset grows.
   
     Query Cache Behavior:
   
        - If your application heavily relies on caching mechanisms, fewer memory resources might be required for query execution.
   
        Misalignment of Instance Size:
   
           - A B2s instance might be over-provisioned for your workload. Your current usage pattern might not demand the full capabilities of the instance.
   

Recommendations:

1. Analyze Database Metrics:
   • Check additional metrics like CPU usage, disk I/O, and query execution times. If other metrics are spiking, it might indicate that low memory usage is not the actual problem.
2. Review Query Patterns:
   • Use the slow query log (log_slow_slave_statements) to identify any queries that might be causing bottlenecks.
3. Increase Buffer Pool Size:
   • Try increasing the innodb_buffer_pool_size parameter within the available memory limit to see if performance improves. Currently, the default might be set too low.
4. Traffic and Query Volume:
   • Correlate memory usage with peak traffic hours to determine if the workload truly stresses the database.
5. Enable Performance Insights:
   • Use Azure’s MySQL Performance Recommendations to assess if the database can perform better with adjusted parameters.
6. Scaling Down:
   • If memory usage is consistently low across high traffic periods, consider scaling down to a lower-tier plan to save costs.

Tools to Help:

• Query Performance Insights: Provided by azure db for MySQL.
• Azure Metrics & Alerts: Set alerts for abnormal memory usage patterns.
• MySQL Slow Query Log: Identify and optimize queries.

Please feel free to click the 'Upvote' (Thumbs-up) button and 'Accept as Answer'. This helps the community by allowing others with similar queries to easily find the solution.

Answer 2

Hello Luong, Welcome to MS Q&A

The MySQL database on the B2s plan may be using only 37% of its memory despite high traffic due to several factors. One possibility is that the memory allocation for buffers and caches may not be fully utilized, which is common in MySQL configurations. Azure Database for MySQL Flexible Server typically consumes memory to maximize cache hits, and memory utilization can hover between 80-90% under normal circumstances. If the memory usage is significantly lower, it could indicate that the configured buffers are too small, or that the queries being executed are not optimized for memory usage.

Additionally, if the maximum connections on the database server are set too low, it could limit the number of concurrent connections and thus the overall memory usage. Monitoring other metrics such as Host CPU Percent, Total Connections, and IO Percent can help determine if there is a sudden spike in workload that might affect memory utilization.

For more detailed troubleshooting, you can refer to the following resources:

• Troubleshoot low memory issues in Azure Database for MySQL - Flexible Server
• Azure Database for MySQL - Flexible Server service tiers

Please let us know if any questions

Kindly accept answer if it helps

Thanks

Deepanshu