Struct vs Dict performance test - Cairo

[danilowhk]

Comparing Updating Struct vs Inserting in Dict: A Benchmark

Introduction

This report compares the gas cost of maintaining and changing values on a struct against inserting new values into a dictionary (Dict) in Cairo. The tests were conducted using scarb 0.6.0-alpha.2 and cairo 2.1.0-rc2.

Obs: For this test, both initialization of the struct and the dict were added on the tests (Dict initialization cost 15420 gas, and struct initialization didn't change the gas)

Methodology

The benchmarks were conducted under the following configurations:

• Language: Cairo
• Version: scarb 0.6.0-alpha.2, cairo 2.1.0-rc2
• Operations: 20 different changes/insertions were evaluated
• Metrics: Gas consumption

Overall Result

The comparison highlights a significant difference in gas consumption:
```

Approach	Gas Consumption
Updating Struct	57470
Inserting in Dict	131040
```

Test with Updating Struct

Description

This approach involves maintaining and changing values on a struct. Each change on the struct is performed 20 times.

Code

#[test]
#[available_gas(1000000)]
fn test_updating_struct(){
    let x = testing::get_available_gas();
    gas::withdraw_gas().unwrap();
    
    
    let mut test_struct = TestStruct { a: 0, b:  2,c:  3, d: 10, e: 20, f:  3, g: 10, h: 20, ab: 1, abc: 2 };
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;        
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;    
    test_struct.a = test_struct.a + 1;
    test_struct.a = test_struct.a + 1;

    '---------Gas Struct---------'.print();
    // 57470 gas for 20 changes, 54820 gas for 19 changes , 2650 gas per change
    (x - testing::get_available_gas()).print();
}

Result

Gas consumption for this test was 57470.

Test with Inserting in Dict

Description

This approach involves inserting new values into a dictionary (Dict). Each insertion is performed 20 times. An insert on Dict takes around 5000 gas units.

Code

#[test]
#[available_gas(1000000)]
fn test_updating_dict(){
    let x = testing::get_available_gas();
    gas::withdraw_gas().unwrap();    
   let mut balances: Felt252Dict<u64> = Default::default();

    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);   
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);   
    balances.insert(1, balances.get(1) + 1);
    balances.insert(1, balances.get(1) + 1);


    '---------Gas Dict---------'.print();
    // 131040 gas for 20 changes, 125430 gas for 19 changes , 5610 gas per change
    (x - testing::get_available_gas()).print();

}

Result

Gas consumption for this test was 131040.

Conclusion

The tests indicate that maintaining and changing values on a struct (57470 gas) is cheaper than inserting new values into a dictionary (131040 gas) in the given setup and conditions. This result highlights the potential efficiency gains of using structs when handling multiple changes in Cairo.

Appendix:

Versions used:

scarb: 0.6.0-alpha.2 (4b4d5411b 2023-07-25)
cairo: 2.1.0-rc2 (https://crates.io/crates/cairo-lang-compiler/2.1.0-rc2)

[Eikix]

I have a question: are dicts and structs even comparable?
Why are we comparing them?

[danilowhk]

It was to compare bigger Data Types that are "mutable", in our case if we should use one or another to store some data such as program counter , gas , etc..