# How to send multiple user operations in parallel

permissionless.js library lets you to send multiple transactions in parallel. This can be useful if you want to batch multiple calls in a single user operation or if you want to send user operations concurrently.

## Batching Multiple Calls

To batch multiple calls in a single user operation, you can use the `sendTransactions` method.

```ts
const transactionHash = await smartAccountClient.sendTransaction({
	calls: [
		{
			to: "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
			value: parseEther("0.1"),
			data: "0x",
		},
		{
			to: "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
			value: parseEther("0.1"),
			data: "0x",
		},
	],
})
```

## Sending Multiple User Operations in Parallel

In an Externally Owned Account (EOA), the `nonce` is a simple incrementing number. However, in smart accounts, the `nonce` consists of two components: a `key` and a `sequence`:

* 192-bit “key”
* 64-bit “sequence”

For each unique `key`, the sequence must be incremented by 1 for each transaction. This means that if you send multiple transactions in parallel, you can use different `keys` for the parallel transactions.

### Parallel Transactions Ordering

Important thing to note is that parallel transaction's ordering is not guaranteed. So execution of random `key` on chain could be:

* \[key-C]\[sequence-0]
* \[key-A]\[sequence-0]
* \[key-B]\[sequence-0]

While execution of `sequence` for a specific `key` will always be in order. So the following is a valid order of execution:

1. \[key-C]\[sequence-0]
2. \[key-A]\[sequence-0]
3. \[key-C]\[sequence-1]
4. \[key-B]\[sequence-0]
5. \[key-A]\[sequence-1]
6. \[key-B]\[sequence-1]

:::info
Note: Pimlico bundler currently only support up to 100 parallel transactions. If you need to send more feel free to contact us at [support@pimlico.io](mailto\:support@pimlico.io).
:::

In the example below, we use the current timestamp as the `key` to send parallel transactions. You can use any other value as the `key`.

```ts
import { encodeNonce } from "permissionless/utils"

const parallelNonce1 = encodeNonce({
	key: BigInt(Date.now()),
	sequence: 0n,
})

const transaction1 = smartAccountClient.sendTransaction({
	calls: [
		{
			to: "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
			value: parseEther("0.1"),
			data: "0x",
		},
		{
			to: "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
			value: parseEther("0.1"),
			data: "0x",
		},
	],
	nonce: parallelNonce1,
})

const parallelNonce2 = encodeNonce({
	key: BigInt(Date.now()),
	sequence: 0n,
})

const transaction2 = smartAccountClient.sendTransaction({
	calls: [
		{
			to: "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
			value: parseEther("0.1"),
			data: "0x",
		},
		{
			to: "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
			value: parseEther("0.1"),
			data: "0x",
		},
	],
	nonce: parallelNonce2,
})

const hashes = await Promise.all([transaction1, transaction2])
```

:::info
Note: The flow described in this section is only applicable to smart accounts that are already deployed, if your account is not deployed, you may run into AA10 errors as multiple userOperations will contain the factory/factoryData fields which will cause conflicts.
:::

This way, you can efficiently manage multiple transactions either sequentially or concurrently.