📩Sending Transactions on Solana

Optimize your transactions to minimize confirmation latency and maximize delivery rates.

Helius' staked connections guarantee 100% transaction delivery with minimal confirmation times.

Summary

We recommend the following best practices to help you land transactions:

• Use Staked Connections available with standard paid plans.

• Use commitment "processed" or "confirmed" to fetch the latest blockhash

• Add priority fees and calculate them dynamically

• Optimize compute unit (CU) usage

• Set maxRetries to 0 and implement robust retry logic

• Send with skipPreflight set to true

Want to go deeper? We cover all fundamentals in this blog post.

Recommended Optimizations for Traders

We recommend the following optimizations for latency-sensitive traders. You must already be applying the best practices for sending transactions mentioned above.

1. Send transactions from Eastern US or Western Europe.

   1. Choose Frankfurt or Pittsburg if you want to co-locate with Helius transaction-sending servers.

   2. Avoid sending regions far away from the validator network (e.g. LATAM or South Africa).

2. Warm the Helius regional caches to minimize tail latency.

   1. Send a getHealth call every second using the same endpoint & API key you use for sending transactions.

   2. Only one warming thread is required per region. Any more will have zero benefit.

The benefits will only be noticeable to experienced traders. We recommend the Sending Smart Transactions section instead for app developers.

Staked Connections

Staked Connections help you land transactions faster with an increased land rate. Helius provides two methods to access staked connections with any standard paid plan (not available on Dedicated Nodes).

1. Shared Staked Endpoint (default)

   • Requirements:

     • Priority fees meet or exceed the recommended value provided by the Priority Fee API

     • Set maxRetries to 0

   • Endpoint: https://mainnet.helius-rpc.com/?api-key=xxx

   • Cost: 1 credit per request

   • Tips:

     • Check if you're getting staked connections by logging the X-Helius-ConnectionType response header. The value will be regular or staked.

2. Dedicated Staked Endpoint

   • Transactions will be sent over staked connections via an optimized network (Asia, Europe, and North America), minimizing latency and confirmation times.

   • Endpoint: https://staked.helius-rpc.com?api-key=xxx

   • Cost: 50 credits per request or a monthly subscription add-on (starts at $4,000/month, contact our sales team for access).

Usage metrics display staked endpoint calls as sendTransactionWithStake to avoid collisions with regular sendTransaction.

Sending Smart Transactions

Both the Helius Node.js and Rust SDKs can send smart transactions. This new method builds and sends an optimized transaction while handling its confirmation status. Users can configure the transaction's send options, such as whether the transaction should skip preflight checks.

At the most basic level, users must supply their keypair and the instructions they wish to execute, and we handle the rest.

We:

• Fetch the latest blockhash

• Build the initial transaction

• Simulate the initial transaction to fetch the compute units consumed

• Set the compute unit limit to the compute units consumed in the previous step, with some margin

• Get the Helius recommended priority fee via our Priority Fee API

• Set the priority fee (microlamports per compute unit) as the Helius recommended fee

  • Adds a small safety buffer fee in case the recommended value changes in the next few seconds

• Build and send the optimized transaction

• Return the transaction signature if successful

Requiring the recommended value (or higher) for our staked connections ensures that Helius sends high-quality transactions and that we won't be rate-limited by validators.

This method is designed to be the easiest way to build, send, and land a transaction on Solana. Note that by using the Helius recommended fee, transactions sent by Helius users on one of our standard paid plans will be routed through our staked connections, guaranteeing nearly 100% transaction delivery.

Node.js SDK

The sendSmartTransaction method is available in our Helius Node.js SDK for versions >= 1.3.2. To update to a more recent version of the SDK, run npm update helius-sdk.

The following example transfers SOL to an account of your choice. It leverages sendSmartTransaction to send an optimized transaction that does not skip preflight checks

import { Helius } from "helius-sdk";
import {
  Keypair,
  SystemProgram,
  LAMPORTS_PER_SOL,
  TransactionInstruction,
} from "@solana/web3.js";

const helius = new Helius("YOUR_API_KEY");

const fromKeypair = /* Your keypair goes here */;
const fromPubkey = fromKeypair.publicKey;
const toPubkey = /* The person we're sending 0.5 SOL to */;

const instructions: TransactionInstruction[] = [
  SystemProgram.transfer({
    fromPubkey: fromPubkey,
    toPubkey: toPubkey,
    lamports: 0.5 * LAMPORTS_PER_SOL, 
  }),
];

const transactionSignature = await helius.rpc.sendSmartTransaction(instructions, [fromKeypair]);
console.log(`Successful transfer: ${transactionSignature}`);

Rust SDK

The send_smart_transaction method is available in our Rust SDK for versions >= 0.1.5. To update to a more recent version of the SDK, run cargo update helius.

The following example transfers 0.01 SOL to an account of your choice. It leverages send_smart_transaction to send an optimized transaction that skips preflight checks and retries twice, if necessary:

use helius::types::*;
use helius::Helius;
use solana_sdk::{
    pubkey::Pubkey,
    signature::Keypair,
    system_instruction
};

#[tokio::main]
async fn main() {
    let api_key: &str = "YOUR_API_KEY";
    let cluster: Cluster = Cluster::MainnetBeta;
    let helius: Helius = Helius::new(api_key, cluster).unwrap();
    
    let from_keypair: Keypair = /* Your keypair goes here */;
    let from_pubkey: Pubkey = from_keypair.pubkey();
    let to_pubkey: Pubkey = /* The person we're sending 0.01 SOL to */;

    // Create a simple instruction (transfer 0.01 SOL from from_pubkey to to_pubkey)
    let transfer_amount = 100_000; // 0.01 SOL in lamports
    let instruction = system_instruction::transfer(&from_pubkey, &to_pubkey, transfer_amount);

    // Create the SmartTransactionConfig
    let config = SmartTransactionConfig {
        instructions,
        signers: vec![&from_keypair],
        send_options: RpcSendTransactionConfig {
            skip_preflight: true,
            preflight_commitment: None,
            encoding: None,
            max_retries: Some(2),
            min_context_slot: None,
        },
        lookup_tables: None,
    };

    // Send the optimized transaction
    match helius.send_smart_transaction(config).await {
        Ok(signature) => {
            println!("Transaction sent successfully: {}", signature);
        }
        Err(e) => {
            eprintln!("Failed to send transaction: {:?}", e);
        }
    }
}

Sending Transactions Without the SDK

We recommend sending smart transactions with one of our SDKs but the same functionality can be achieved without using one. Both the Node.js SDK and Rust SDK are open-source, so the underlying code for the send smart transaction functionality can be viewed anytime.

Prepare and Build the Initial Transaction

First, prepare and build the initial transaction. This includes creating a new transaction with a set of instructions, adding the recent blockhash, and assigning a fee payer. For versioned transactions, create a TransactionMessage and compile it with lookup tables if any are present. Then, create a new versioned transaction and sign it — this is necessary for the next step when we simulate the transaction, as the transaction must be signed.

For example, if we wanted to prepare a versioned transaction:

// Prepare your instructions and set them to an instructions variable
// The payerKey is the public key that will be paying for this transaction
// Prepare your lookup tables and set them to a lookupTables variable

let recentBlockhash = (await this.connection.getLatestBlockhash()).blockhash;

const v0Message = new TransactionMessage({
    instructions: instructions,
    payerKey: pubKey,
    recentBlockhash: recentBlockhash,
}).compileToV0Message(lookupTables);

versionedTransaction = new VersionedTransaction(v0Message);
versionedTransaction.sign([fromKeypair]);

Optimize the Transaction's Compute Unit (CU) Usage

To optimize the transaction's compute unit (CU) usage, we can use the simulateTransaction RPC method to simulate the transaction. Simulating the transaction will return the amount of CUs used, so we can use this value to set our compute limit accordingly. It's recommended to use a test transaction with the desired instructions first, plus an instruction that sets the compute limit to 1.4m CUs. This is done to ensure the transaction simulation succeeds. For example:

const testInstructions = [
    ComputeBudgetProgram.setComputeUnitLimit({ units: 1_400_000 }),
    ...instructions,
];

const testTransaction = new VersionedTransaction(
    new TransactionMessage({
        instructions: testInstructions,
        payerKey: payer,
        recentBlockhash: (await this.connection.getLatestBlockhash()).blockhash,
    }).compileToV0Message(lookupTables)
);

const rpcResponse = await this.connection.simulateTransaction(testTransaction, {
    replaceRecentBlockhash: true,
    sigVerify: false,
});

const unitsConsumed = rpcResponse.value.unitsConsumed;

It is also recommended to add a bit of margin to ensure the transaction executes without any issues. We can do so by setting the following:

let customersCU = Math.ceil(unitsConsumed * 1.1);

Then, create an instruction that sets the compute unit limit to this value and add it to your array of instructions:

const computeUnitIx = ComputeBudgetProgram.setComputeUnitLimit({
    units: customersCU
});

instructions.push(computeUnitIx);

Serialize and Encode the Transaction

This is relatively straightforward. First, to serialize the transaction, both Transaction and VersionedTransaction types have a .serialize() method. Then use the bs58 package to encode the transaction. Your code should look something like bs58.encode(txt.serialize());

Setting the Right Priority Fee

First, use the Priority Fee API to get the priority fee estimate. We want to pass in our transaction and get the Helius recommended fee via the recommended parameter:

const response = await fetch(HeliusURL, {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({
        jsonrpc: "2.0",
        id: "1",
        method: "getPriorityFeeEstimate",
        params: [
            {
                transaction: bs58.encode(versionedTransaction), // Pass the serialized transaction in
                options: { recommended: true },
            },
        ],   
    }),
});

const data = await response.json();
const priorityFeeRecommendation = data.result.priorityFeeEstimate;

Then, create an instruction that sets the compute unit price to this value, and add that instruction to your previous instructions:

const computeBudgetIx = ComputeBudgetProgram.setComputeUnitPrice({
    microLamports: priorityFeeRecommendation,
});

instructions.push(computeBudgetIx);

Build and Send the Optimized Transaction

This step is almost a repeat of the first step. However, the array of initial instructions has been altered to add two instructions to set the compute unit limit and price optimally. Now, send the transaction. It doesn't matter if you send with or without preflight checks or change any other send options — the transaction will be routed through our staked connections.

Polling the Transaction's Status and Rebroadcasting

While staked connections will forward a transaction directly to the leader, it is still possible for the transaction to be dropped in the Banking Stage. It is recommended that users employ their own rebroadcasting logic rather than rely on the RPC to retry the transaction for them.

The sendTransaction RPC method has a maxRetries parameter that can be set to override the RPC's default retry logic, giving developers more control over the retry process. It is a common pattern to fetch the current blockhash via getLatestBlockhash, store the lastValidBlockHeight, and retry the transaction until the blockhash expires. It is crucial to only re-sign a transaction when the blockhash is no longer valid, or else it is possible for both transactions to be accepted by the network.

Once a transaction is sent, it is important to poll its confirmation status to see whether the network has processed and confirmed it before retrying. Use the getSignatureStatuses RPC method to check a list of transactions' confirmation status. The @solana/web3.js SDK also has a getSignatureStatuses method on its Connection class to fetch the current status of multiple signatures.

How sendSmartTransaction Handles Polling and Rebroadcasting

The sendSmartTransaction method has a timeout period of 60 seconds. Since a blockhash is valid for 150 slots, and assuming perfect 400ms slots, we can reasonably assume a transaction's blockhash will be invalid after one minute. The method sends the transaction and polls its transaction signature using this timeout period:

try {
   // Create a smart transaction
   const transaction = await this.createSmartTransaction(instructions, signers, lookupTables, sendOptions);
  
   const timeout = 60000;
   const startTime = Date.now();
   let txtSig;
  
   while (Date.now() - startTime < timeout) {
     try {
       txtSig = await this.connection.sendRawTransaction(transaction.serialize(), {
         skipPreflight: sendOptions.skipPreflight,
         ...sendOptions,
       });
  
       return await this.pollTransactionConfirmation(txtSig);
     } catch (error) {
       continue;
     }
   }
} catch (error) {
   throw new Error(`Error sending smart transaction: ${error}`);
}

txtSig is set to the signature of the transaction that was just sent. The method then uses the pollTransactionConfirmation() method to poll the transaction's confirmation status. This method checks a transaction's status every five seconds for a maximum of three times. If the transaction is not confirmed during this time, an error is returned:

async pollTransactionConfirmation(txtSig: TransactionSignature): Promise<TransactionSignature> {
    // 15 second timeout
    const timeout = 15000;
    // 5 second retry interval
    const interval = 5000;
    let elapsed = 0;

    return new Promise<TransactionSignature>((resolve, reject) => {
      const intervalId = setInterval(async () => {
        elapsed += interval;

        if (elapsed >= timeout) {
          clearInterval(intervalId);
          reject(new Error(`Transaction ${txtSig}'s confirmation timed out`));
        }

        const status = await this.connection.getSignatureStatuses([txtSig]);

        if (status?.value[0]?.confirmationStatus === "confirmed") {
          clearInterval(intervalId);
          resolve(txtSig);
        }
      }, interval);
   });
}

We continue sending the transaction, polling its confirmation status, and retrying it until a minute has elapsed. If the transaction has not been confirmed at this time, an error is thrown.