Performance and Advanced Usage

This guide covers advanced features designed to speed up your local testing workflow and verify the performance of the precompile shims.

Speeding Up Tests with RPC Caching

When you use the arb:reseed-shims task with the --stylus flag, the plugin fetches the latest gas price data from a live RPC endpoint. Making a network call every time you run your tests can be slow.

To significantly speed this up, you can enable RPC caching.

How Caching Works

When enabled, the plugin saves the fetched gas-price tuple to a local file. On subsequent runs, if the cache is still valid, the plugin reads from the file instead of making a network call, resulting in a much faster reseeding process.

Cache File Location: The cache is stored at .cache/stylus-prices.json in your project root.
Activation: Caching is activated by adding the --cache-ttl <seconds> flag to the reseed command.

Usage Example

First Run (Cache Miss): Run the reseed task with a Time-To-Live (TTL) for the cache (e.g., 600 seconds / 10 minutes). The task will fetch data from the RPC and create the cache file.

BASH

STYLUS_RPC=[https://sepolia-rollup.arbitrum.io/rpc](https://sepolia-rollup.arbitrum.io/rpc) \
npx hardhat arb:reseed-shims --network localhost --stylus --cache-ttl 600

Expected Output:

TEXT

ℹ️ fetched from Stylus: [...]
✅ Re-seeded getPricesInWei -> [...]

Second Run (Cache Hit): Run the same command again within the 10-minute TTL. This time, it reads from the local cache, skipping the network request. You can even run it without the STYLUS_RPC variable set.

BASH

npx hardhat arb:reseed-shims --network localhost --stylus --cache-ttl 600

Expected Output:

TEXT

ℹ️ using Stylus file cache: [...]
✅ Re-seeded getPricesInWei -> [...]

Benchmarking Local Performance

The precompile shims are designed to be extremely lightweight. To help you verify their performance, the plugin includes a micro-benchmark script. This script runs a high number of sequential reads against the ArbGasInfo shim to measure its latency.

How to Run the Benchmark

Use the following command to execute 1,000 sequential eth_call reads. You can change the value of N to run more or fewer iterations.

BASH

N=1000 npx hardhat run --network localhost scripts/micro-bench-gasinfo.js

Expected Output (will vary by machine):

TEXT

Reads: 1000, total ms: 1746, avg ms/read: 1.746

This demonstrates the negligible overhead of the shim, ensuring it won't slow down your test suite.

Future Feature: Gas Cost Accounting

To better simulate on-chain behavior, a future version of the plugin will introduce realistic gas cost accounting for precompile calls. The configuration for this feature is reserved but has no effect in the current shim-only mode.

Reserved Configuration (hardhat.config.js)

// This configuration is for a future feature and is currently a no-op.
arbitrum: {
  costing: {
    enabled: false,
    emulateNitro: false
  }
}

In the current version, calls to the shims via eth_call do not report gasUsed.

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