Solana Transactions and Address Lookup Tables

Use this skill when working with Solana transaction size limits, Address Lookup Tables (ALTs), and VersionedTransactions.

Transaction Size Limit

Solana transactions have a hard limit of 1232 bytes. This includes:

•Signatures (64 bytes each)
•Message header (3 bytes)
•Account addresses (32 bytes each, unless using ALT)
•Instructions (variable)

When ALT is Needed

Calculate transaction size:

•Each account = 32 bytes (without ALT) or 1 byte (with ALT)
•Large instructions (like CCTP messages ~400+ bytes) leave less room for accounts

Example: CCTP receiveMessage with 20 accounts:

•Without ALT: ~1474 bytes (EXCEEDS LIMIT)
•With ALT: ~916 bytes (OK)

Address Lookup Tables (ALT)

ALTs store frequently-used addresses on-chain. Transactions reference them by 1-byte index instead of 32-byte address.

Creating an ALT

typescript

import { AddressLookupTableProgram, Connection, Keypair } from "@solana/web3.js";

// 1. Create the ALT
const [createIx, altAddress] = AddressLookupTableProgram.createLookupTable({
  authority: payer.publicKey,
  payer: payer.publicKey,
  recentSlot: await connection.getSlot(),
});

// 2. Extend with addresses
const extendIx = AddressLookupTableProgram.extendLookupTable({
  payer: payer.publicKey,
  authority: payer.publicKey,
  lookupTable: altAddress,
  addresses: [address1, address2, ...],  // Max ~30 per instruction
});

// 3. Wait for activation (~1 slot)

Using an ALT in Transactions

typescript

import { TransactionMessage, VersionedTransaction } from "@solana/web3.js";

// Fetch ALT from chain
const altAccountInfo = await connection.getAddressLookupTable(altAddress);
const addressLookupTable = altAccountInfo.value;

// Build VersionedTransaction
const messageV0 = new TransactionMessage({
  payerKey: user,
  recentBlockhash: blockhash,
  instructions,
}).compileToV0Message([addressLookupTable]);

const versionedTx = new VersionedTransaction(messageV0);

Legacy vs Versioned Transactions

Feature	Legacy Transaction	VersionedTransaction (v0)
ALT support	No	Yes
Max accounts	~35 (size limited)	256 (with ALT)
Wallet support	Universal	Most modern wallets

Type Guard

typescript

function isVersionedTransaction(
  tx: Transaction | VersionedTransaction
): tx is VersionedTransaction {
  return "version" in tx;
}

ALT Best Practices

•Include static addresses only - Program IDs, PDAs that don't change
•Don't include dynamic addresses - User wallets, ATAs vary per transaction
•Validate before use - Check ALT exists and has expected address count
•Fallback to legacy - If ALT unavailable, try legacy (may fail for large txs)

typescript

async function fetchAlt(connection, altAddress) {
  const info = await connection.getAddressLookupTable(altAddress);
  if (!info.value || info.value.state.addresses.length < expectedCount) {
    return null; // Fallback to legacy
  }
  return info.value;
}

Sending Transactions

typescript

// Works for both legacy and versioned
const signature = await connection.sendRawTransaction(
  signedTransaction.serialize(),
  { skipPreflight: false, preflightCommitment: "confirmed" }
);