Workload Engine

The workload engine generates transaction load at a target gas rate. Workloads are defined by gas/sec, not requests/sec — this accurately models blockchain resource consumption since different transaction types consume vastly different amounts of gas.

Ref: RFC-0005.

Gas Rate Modes

The engine supports four gas rate modes, each computing the target gas/sec for a given elapsed time.

Mode	Fields	Behavior
`Sustained`	`gas_per_sec`	Constant rate
`Ramped`	`start_gas_per_sec`, `end_gas_per_sec`, `duration_ms`	Linear interpolation between start and end
`Bursty`	`baseline_gas_per_sec`, `burst_peak_gas_per_sec`, `burst_duration_ms`, `burst_interval_ms`	Periodic bursts above a baseline
`Custom`	`schedule: Vec<(u64, u64)>`	Arbitrary piecewise-linear schedule

The engine evaluates the rate on each tick (TICK_INTERVAL_MS) and generates enough transactions to consume the target gas for that interval.

Transaction Templates

Templates define the shape of a transaction. Each template implements the Parameterizer trait:

#![allow(unused)]
fn main() {
trait Parameterizer: Send + Sync {
    fn descriptor(&self) -> TemplateDescriptor;
    fn next(&mut self, rng: &mut impl Rng, to: Address) -> TemplateOutput;
}
}

Every call to next() returns a TemplateOutput with to, value, data, gas_limit, estimated_gas, and template_name.

Built-in Templates

Template	Est. Gas	Description
`simple-transfer`	21,000	ETH value transfer
`noop`	21,000	Zero-value self-transfer
`erc20-transfer`	~65,000	ERC-20 `transfer()`
`erc20-approve`	~46,000	ERC-20 `approve()`
`storage-write`	~44,000	Single storage slot write
`storage-write-heavy`	~200,000	Multiple storage slot writes
`compute-heavy`	~200,000	CPU-intensive loop
`calldata-heavy`	configurable	Large calldata payload

All calldata includes the CALLDATA_MAGIC bytes [0x47, 0x48, 0x4D, 0x52] (“GHMR”) for on-chain attribution.

Template Weighting

Scenarios assign integer weights to templates. The engine normalizes weights into a probability distribution and selects templates proportionally.

templates:
  - name: simple-transfer
    weight: 70
  - name: erc20-transfer
    weight: 30

This produces ~70% transfers and ~30% ERC-20 calls by count, though the gas distribution will differ due to different per-tx gas costs.

Account Pool

Test accounts are derived deterministically from an HD wallet mnemonic.

Derivation path: m/44'/60'/0'/0'/0x4748/{index}

The 0x4748 segment is the GasHammer DNA marker (“GH” in hex). This makes GasHammer-generated accounts identifiable on-chain.

Key properties:

Deterministic: same mnemonic + same index = same private key.
Partitioned: accounts are divided across edges with no overlap.
Nonce-tracking: each Account maintains a local nonce counter, avoiding on-chain queries. On tx failure, the nonce is not incremented.
Thread-safe: Account::next_nonce() uses AtomicU64 for lock-free increment.

Deterministic PRNG

All randomness in workload generation (template selection, parameter variation, account assignment) flows through a seeded ChaCha8Rng. The same seed value with the same scenario configuration produces the same transaction sequence, enabling reliable comparison across runs.

The seed is set in the scenario:

workload:
  seed: 42

Default seed is 0 if omitted.

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