Serde Cow vs String Performance Comparison

I saw an article serde's borrowing can be treacherous and I was curious about the performance impact of using Cow<'a, str> instead of String as I have always used String in my code because it is very convenient. The article suggested using Cow<'a, str> as a potential solution to avoid unnecessary allocations. While it may seem like it makes perfect sense to not allocate when possible, this benchmark aims to evaluate whether using Cow<'a, str> actually provides a performance benefit over using String directly.

All code can be found on Github.

# Benchmark Setup

The benchmark is run using the criterion crate. The benchmark is run with the following parameters:

• NUM_OBJECTS: 1,000,000
• STRING_SIZE: 200

JSON is generated using the following methods:

• generate_happy_path_json: Generates a JSON array of objects with simple strings (happy path - no escaping needed)
• generate_partial_escaped_json: Generates a JSON array where some objects have escaped strings
• generate_pathological_json: Generates a JSON array where all objects have escaped strings (pathological case)

# Machine

• CPU: AMD Ryzen 7 5800X3D @ 4.5GHz
• RAM: 32GB DDR4 3200MHz
• Storage: WD_BLACK SN850X 1TB NVMe SSD
• Kernel: 6.17.9-arch1-1

# Formatted Results

# Happy Path (No Escaping Needed)

# Partial Escaped (Some Objects Need Escaping)

# Pathological Case (All Objects Need Escaping)