> ## Documentation Index
> Fetch the complete documentation index at: https://docs.optimism.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Changing gas target/limit

> Learn how to change the gas target and limit on your OP Stack chain.

This guide covers how to optimize block processing performance at higher gas limits, test your infrastructure before activation, and safely change the gas target and/or limit on a live chain.
This guide assumes your OP Stack chain has the [Holocene features](/notices/archive/holocene-changes) activated.

## Recommended config for best performance

Some known ways to improve block processing performance:

* **Use NVMe for storage** instead of local SSDs or other persistent disks
* **Use full nodes where possible** over archive nodes

## Pre-activation testing

To ensure your chain and supporting infrastructure can consistently process blocks up to your gas limit, you should run some performance tests.
You'll want to run benchmarks and perform careful analysis of the results to ensure your execution clients can handle the increased gas usage.

## Changing the gas target/limit change

How to change the gas target/limit on a live chain.

### Relevant configuration parameters

The gas configuration on an OP Stack chain use the same EIP-1559 parameters as Ethereum.
Where the **gas target** = **gas limit** / **elasticity**.
These values can be found in the `SystemConfig` contract.

### Procedure

Holocene introduces the ability to change the EIP-1559 parameters `elasticity` and `denominator` via the `SystemConfig`. This will allow you to set proper values for the `elasticity` and block `gasLimit`.

**Example**: to double the *target* while keeping the block *limit* at 30Mgas/block:

<Steps>
  <Step title="Retrieve existing EIP-1559 values">
    Retrieve the existing `eip1559Elasticity` and `eip1559Denominator` values:

    ```solidity theme={null}
    elasticity = SystemConfig.eip1559Elasticity() // 6
    denominator = SystemConfig.eip1559Denominator() // 50
    limit = SystemConfig.gasLimit() // 30_000_000 gas, 30Mgas    
    ```

    Current target = `30Mgas / 6 = 5Mgas per block`
  </Step>

  <Step title="Set new EIP-1559 params">
    Use value from previous step as input to set new params and reduce the `elasticity` from `6` to `3`:

    ```solidity theme={null}
    SystemConfig.setEIP1559Params(denominator, 3)
    ```

    New target = `30Mgas / 3 = 10Mgas per block`
  </Step>
</Steps>

## Post-activation monitoring

What to monitor after executing the gas changes.

### SystemConfig contract values

* `SystemConfig.gasLimit()`
* `SystemConfig.eip1559Denominator()`
* `SystemConfig.eip1559Elasticity()`

### Block explorer

For example, on [OP Mainnet](https://optimistic.etherscan.io/blocks):

* Any block with `gasUsed > gasTarget` should cause the base fee to increase
* Any block with `gasUsed < gasTarget` should cause the base fee to decrease

### Node performance

* Verify nodes are processing blocks faster than the block period
* Monitor CPU/memory usage and p99 tail latency of block processing