Benchmark: V8 garbage collection vs out-of-scope access cost

Script Preparation code:

var k1 = 0, k2 = 1, k3 = 2;
var k = () => {
  k1 = k2 + k3;
  k2 = k1 + k3;
  k1 = k2 + k3;
  k3 = k1 + k1;
  return k1 + k2 + k3;
};
var _k = () => {
  let _k1 = 0, _k2 = 1, _k3 = 2;
  _k1 = _k2 + _k3;
  _k2 = _k1 + _k3;
  _k1 = _k2 + _k3;
  _k3 = _k1 + _k1;
  return _k1 + _k2 + _k3;
}

Tests:

garbage collection
_k();
out of scope access
k();

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
garbage collection
out of scope access

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.5 Safari/605.1.15

Browser/OS: Safari 17 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
garbage collection	8502131.0 Ops/sec
out of scope access	496571.9 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**Benchmark Description**

The benchmark compares the performance cost of garbage collection in V8 (a JavaScript engine used by Google Chrome) when accessing variables that are out of scope versus when accessing variables within scope.

**Script Preparation Code**

The script preparation code defines two functions, `k()` and `_k()`. Both functions assign values to variables `k1`, `k2`, `k3` and perform arithmetic operations on these variables. The difference lies in the scoping:

- In the `k()` function, variables are declared with `var` (hoisted) outside of any function. This means they are accessible throughout the execution of the function.
- In the `_k()` function, variables are declared with `let` (block-scoped) inside a function. The `_k1`, `_k2`, and `_k3` variables are only accessible within this scope.

**Benchmark Definition**

The benchmark consists of two test cases:

1. **Garbage Collection**: This test case runs the `_k()` function, which is not referenced outside its scope. This means that after each iteration of the function, the variables `k1`, `k2`, and `k3` will be garbage collected, as they are no longer in use.
2. **Out-of-Scope Access**: This test case runs the `k()` function, which is declared with `var` outside a function, making these variables globally accessible.

**Options Compared**

The two options being compared are:

- **Garbage Collection (GC)**: V8's garbage collection mechanism automatically reclaims memory occupied by objects that are no longer referenced.
- **Out-of-Scope Access**: Directly accessing and modifying global variables without any scope or referencing mechanism.

**Pros and Cons**

- **Garbage Collection (GC)**:
  - Pros:
    - Automatic memory management, reducing the risk of memory leaks.
    - Improves code readability by minimizing global variable usage.
  - Cons:
    - Can introduce overhead due to garbage collection cycles.
    - May cause performance issues if not managed efficiently.

- **Out-of-Scope Access**:
  - Pros:
    - Direct access to variables, potentially improving readability and maintainability.
  - Cons:
    - Increases the risk of memory leaks and makes code harder to understand without proper referencing or scoping mechanisms.
    - Can lead to performance issues if not managed carefully.

**Other Considerations**

- **Library Usage**: None mentioned in this benchmark.
- **JavaScript Features/Syntax**: The use of `var`, `let`, and the function syntax is standard JavaScript features, not specific to any library or feature that requires special explanation.

**Alternatives**

Alternative approaches to measuring performance differences could include:

1. Measuring memory usage over time with instruments like V8's Profiler.
2. Using a different JavaScript engine for comparison (e.g., SpiderMonkey).
3. Comparing caching strategies in the same benchmark, e.g., comparing warm-up caches before running the test cases again.

However, the current approach is focused on highlighting the impact of garbage collection vs out-of-scope access scenarios, making it an informative benchmark for understanding V8's behavior under these specific conditions.

Related benchmarks:

V8 garbage collection vs out-of-scope access cost (version: 0)

Comparing performance of: garbage collection vs out of scope access

Created: 4 years ago by: Guest

Jump to the latest result

garbage collection

out of scope access

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):