# On Chain Registry

## Summary

Stores a registry of Balancer Pool addresses for a given token address pair. Pools can be sorted in order of liquidity and queried via view functions. Used in combination with the [Exchange Proxy](https://balancer.gitbook.io/balancer-v2/v1/smart-contracts/exchange-proxy) swaps can be sourced and exectured entirely on-chain.

## API

### **Adding Pools To Registry**

#### **addPoolPair**

`addPoolPair(address pool, address token1, address token2)`

Adds a single pool address for token pair.

#### addPools

`addPools(address[] calldata pools, address token1, address token2)`

Adds an array of pool addresses for token pair.

### **Sorting Pools**

#### **sortPools**

`sortPools(address[] calldata tokens, uint256 lengthLimit)`

Sorts pools in order of liquidity. lengthLimit can be used to limit the number of pools sorted.

#### sortPoolsWithPurge

`sortPoolsWithPurge(address[] calldata tokens, uint256 lengthLimit)`

Sorts pools in order of liquidity and removes any pools with <10% of total liquidity.

### **Retrieving Pools**

#### **getBestPools**

`getBestPools(address fromToken, address destToken)`

Retrieve array of pool addresses for token pair. Ordered by liquidity if previously sorted. Max of 32 pools returned.

#### getBestPoolsWithLimit

`getBestPoolsWithLimit(address fromToken, address destToken, uint256 limit)`

Retrieve array of pool addresses for token pair. Ordered by liquidity if previously sorted. Max of n pools returned where n=limit.

#### getPoolsWithLimit

`getPoolsWithLimit(address fromToken, address destToken, uint256 offset, uint256 limit)`

Retrieve array of pool addresses using an offset starting position.


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