Every time your program requests new memory (an allocation), there is a performance cost, even if it doesn’t trigger a Garbage Collection (GC).The single most expensive part of this process is memory clearing.
The GC guarantees that any new block of memory it provides is “zeroed out” (every bit is set to zero).
Tip
Analogy: Think of this as getting a perfectly clean, sanitized workspace every time you start a new task.
This is crucial for security and to prevent bugs, but it requires CPU cycles to perform.
How to Measure Allocation Cost 🧪
Directly measuring the cost of every allocation is impractical.
They happen so often that monitoring them would create too much overhead and slow the program down.
Instead, we can measure the cost indirectly in three ways:
-
Count GCs
Since most GCs are triggered by allocations, the frequency of GCs is a good indicator of how much allocation is happening. -
Sampling
Instead of watching every single allocation, profilers can take a small, random sample.
This provides a good statistical picture of allocation costs without the performance hit. -
Check CPU Usage
You can use a profiling tool to see how much CPU time is being spent inside the specific GC functions responsible for memory clearing.
Note
These indirect methods help you balance accuracy with performance impact while profiling.