Improve feeHistory performance

[mattsse]

Describe the feature

currently the feeHistory implementation is very expensive:

it reads the entire recent header range:

reth/crates/rpc/rpc/src/eth/api/fees.rs

Line 94 in a6bee72

let headers = self.provider().sealed_headers_range(start_block..=end_block)?;

and if reward percentiles are provided it computes the reward percentiles based on the request input:

reth/crates/rpc/rpc/src/eth/api/fees.rs

Lines 108 to 111 in a6bee72

	// Percentiles were specified, so we need to collect reward percentile ino
	if let Some(percentiles) = &reward_percentiles {
	rewards.push(self.calculate_reward_percentiles(percentiles, header).await?);
	}

There are two improvements we can make here:

• cache the base fee per gas and gas used ration per block:
  

  reth/crates/rpc/rpc/src/eth/api/fees.rs

  Lines 104 to 106 in a6bee72

  	base_fee_per_gas
  	.push(U256::try_from(header.base_fee_per_gas.unwrap_or_default()).unwrap());
  	gas_used_ratio.push(header.gas_used as f64 / header.gas_limit as f64);

Another improvement we could do is approximating the reward percentiles by computing the rewards with a certain resolution

Additional context

reth/crates/rpc/rpc/src/eth/gas_oracle.rs

Lines 96 to 98 in a6bee72

	/// Stores the latest calculated price and its block hash and Cache stores the lowest effective
	/// tip values of recent blocks
	inner: Mutex<GasPriceOracleInner>,

[allnil]

Hey!
Maybe I could do this?

[mattsse]

awesome,

the second part is probably a bit more complex, but I think we should be fine if we compute a percentiles range with maybe a 0.25 pt resolution so 400 percentile points, so we don't need to recompute them on a per request basis and instead can approximate them with sufficient accuracy.

ptal at the GasOracle, how we cache in there