The Formula

Here’s the formula that the GC uses to figure out what size heap you need:

For example, if the actual memory in use after the garbage collector has done its job is 82MB, that means:

• Live heap: 82 MB (actual memory in use after GC).

• GOGC: 100 (default value, meaning 100%).

• Calculation: $82 \text{ MB} \times (1 + \frac{100}{100}) = 82 \text{ MB} \times 2 = \textbf{164 MB}$

The slight difference might occur due to rounding and internal GC accounting.

This means that the GC won’t run again until the heap grows to ~164 MB. This is Go’s way of balancing:

• Memory usage: Don’t let the heap grow unbounded.

• CPU efficiency: Don’t run GC too frequently (wastes CPU).

Tuning GOGC

You can adjust this behaviour with the GOGC environment variable:

• GOGC=100 (default): Next GC at 2× live heap.

• GOGC=200: Next GC at 3× live heap (less frequent GC, more memory).

• GOGC=50: Next GC at 1.5× live heap (more frequent GC, less memory).

• GOGC=off: Disable automatic GC entirely (not recommended for production).