# Global variables

### Gas price and oracle

{% hint style="info" %}
**Gas price** (given is GWEI units) is a key parameter of Mangrove that [determines the remuneration](https://docs.mangrove.exchange/mangrove-core/taking-and-making-offers/reactive-offer/offer-provision#offer-bounty-computation) of takers for removing a failing offer from a list. In order to make sure takers are consistently over-compensated for the gas used, it should be kept well above average `tx.gasprice`.
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**Gas price** can be read from an outside Monitoring Contract. When the governance wishes to do so, it **must** enable this feature by letting the monitor (if any) act as a gas price oracle. This can be done using the governance restricted function `setUseOracle` of Mangrove.

If monitoring the gas price is not enabled, or if the value returned by the monitor is ill formed, Mangrove will use its global [`gasprice`](https://docs.mangrove.exchange/mangrove-core/technical-references/mangrove-configuration#mgvlib.global) parameter as fallback. 

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{% tab title="Signatures" %}

```solidity
// Governance lets the monitor determine gasprice
function setUseOracle(bool useOracle) public;

// Governance sets the fallback gasprice value (in GWEI)
function setGasprice(uint gasprice) public;

// Governance sets a new monitor
function setMonitor(address monitor) public;
```

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{% tab title="Events" %}

```solidity
event SetGasprice(uint gasprice); // emitted when gas price is updated
event SetMonitor(address monitor); // emitted when a new monitor is set
event SetUseOracle(bool value); // logs `true` if Mangrove is set to use an external monitor to read gasprice. Logs `false` otherwise
```

{% endtab %}
{% endtabs %}

{% hint style="danger" %}
**Important point**

If allowing the monitor to act as a gas price Oracle, Governance **must** have previously deployed a Monitor Contract and set its address in Mangrove's configuration.
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### Other governance controlled setters

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{% tab title="Signature" %}

```solidity
// Governance sets maximum allowed gas per offer
function setGasmax(uint gasmax) public;
// Changing governance address
function setGovernance(address value);
// Changing treasury address
function setVault(address value);
// (de)activates sending trade notification to governance contract (e.g. for rewards programs)
function setNotify(bool value);
// set maximum gas amount an offer may require to execute
function setGasmax(uint value);
// permanently puts mangrove into a killed state (Mangrove rejects all taker and maker orders, only retracting offer is possible)
function kill();

```

{% endtab %}
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