Why Does My Go Program's Reported Memory Usage Exceed Its Heap Profile?

Analyzing Go Runtime Memory

Understanding Memory Usage Discrepancies

When analyzing Go memory using the pprof tool, you may encounter a disparity between the reported heap usage and the actual memory usage of your program. This is because the heap profile only shows active memory, while the reported memory usage includes both active and collected memory.

Alternative Tools for Memory Analysis

If you need a more accurate breakdown of how Go manages memory, you can use the runtime.ReadMemStats function, which provides a detailed report on memory allocation and usage. Additionally, the debugging view of the heap profile in the web-based profiler (accessible via http://10.10.58.118:8601/debug/pprof/) includes a printout of a MemStats structure, giving you further insights into memory distribution.

Factors Influencing Memory Discrepancy

The discrepancy between the heap profile and reported memory usage is caused by several factors:

• Garbage Collection (GC): As the GC collects unused memory, the heap profile shrinks, but the physical memory occupied by the program remains the same.
• Memory Fragmentation: The GC may not be able to reuse previously collected memory due to fragmentation, which can lead to an increase in the allocated memory.
• GC Threshold: The GC runs only when the memory in use doubles the memory in use after the previous GC, which means that significant amounts of memory may not be freed promptly.

Understanding MemStats

The MemStats structure provides detailed information about memory usage:

• HeapAlloc: Active heap memory (essentially, what the heap profile shows).
• Alloc: Memory used by all Go-managed objects, including both active and collected memory.
• Sys: Total memory requested from the OS (including both active and collected memory, as well as memory allocated via CGO/syscall).

It's important to note that there may still be some discrepancies between Sys and the reported memory usage by the OS due to differences in memory allocation between Go and the underlying operating system.

The above is the detailed content of Why Does My Go Program's Reported Memory Usage Exceed Its Heap Profile?. For more information, please follow other related articles on the PHP Chinese website!