Understanding the Source of MySQL Thread Metrics in Foglight (4379540)

This article explains where Foglight obtains thread-related MySQL metrics such as Threads_running, Threads_connected, Threads_cached, and Thread_cache_size, and how they are collected by the MySQL cartridge.

Foglight dashboards display metrics related to MySQL thread pool activity, such as:

• Threads Running
• Threads Connected
• Threads Cached
• Threads Created per Second
• Thread Cache Size
• Thread Pool Hit Rate (%)

Users may want to understand where these metrics originate and how they are collected.

Foglight collects these metrics from the MySQL server using SQL queries during each monitoring cycle. These metrics reflect the status and configuration of the MySQL thread pool and are important for understanding concurrency and connection reuse behavior.

The following table summarizes the source of each thread-related metric collected by the MySQL cartridge:

• SHOW STATUS returns real-time server status metrics.
• SHOW VARIABLES returns configuration values, including thread_cache_size.
• Threads Created per Second is calculated by tracking the delta of Threads_created between two polling intervals.
• Thread Pool Hit Rate (%) is calculated using:

  1 - (Threads_created / Connections)

  expressed as a percentage.

References

• MySQL Documentation – SHOW STATUS
• MySQL Documentation – SHOW VARIABLES
• Foglight for Databases – MySQL Cartridge Implementation Guide