# Sync committees dirtying `state.balances`

[hex-core i7]: https://www.intel.com/content/www/us/en/products/sku/126684/intel-core-i78700k-processor-12m-cache-up-to-4-70-ghz/specifications.html

## Benching a recent mainnet block

These benchmarks involve getting a recent mainnet `BeaconState` (slot `1783731`) and then deriving two `BeaconState` objects:

1. A "clean" state with no changes.
2. A "dirty" state where 512 `state.balances` entries have been incremented by `1`. The changes are evenly distributed across the `state.balances` array.

Then, for each state, we perform a cached tree-hash (with an already initialized cache). Results:

- Clean: 35.642 ms
- Dirty: 37.109 ms

Here, the difference is 1.47 ms. However, the differences vary across runs, it is generally within 1-2ms.

> Caveat: cached tree hashing uses parallelization and the timings are highly dependent on the speed and availability of the CPU. So, whilst the increase here is 4%, mileage will vary. This test was conducted on a [hex-core i7] running many other applications.

Source code for bench: https://github.com/paulhauner/lighthouse/blob/paul-altair-benches/consensus/types/benches/altair_balance_changes.rs