Theo's Typesafe Cult•5mo ago

Throttling calls to a server function in NextJS

I have a server function that can poll if a long-running event (Ethereum transaction being mined) has completed yet. The actual request checking the blockchain is obviously also async and can take a second or two. If someone hits the page when the transaction result hasn't already been stored in the db, their client will start calling a function on the server to check the status and update the db on success. If multiple people are on this page, I don't really want to poll the blockchain excessively, so I want to early exit from calls to the server function that happen too often. Will this approach work?

const lastInvocationTimes = new Map<string, number>();

export async function pollProposalTransactionAndUpdateIfResolved({
  proposalId,
  chainId,
  transactionHash,
}: {
  proposalId: Proposal["id"];
  transactionHash: Hash;
  chainId: number;
}) {
  // unique key for the tx.
  const key = `${chainId}-${transactionHash}`;
  const lastInvocationTime = lastInvocationTimes.get(key);
  
  // Check if on cooldown.
  if (lastInvocationTime && lastInvocationTime + 1000 * 15 > Date.now()) {
    console.debug(`polling ${transactionHash} on ${chainId} throttled`);
    return;
  }

  // Not invoked recently.
  lastInvocationTimes.set(key, Date.now());
  await _pollProposalTransactionAndUpdateIfResolved({
    proposalId,
    chainId,
    transactionHash,
  });
}

const lastInvocationTimes = new Map<string, number>();

export async function pollProposalTransactionAndUpdateIfResolved({
  proposalId,
  chainId,
  transactionHash,
}: {
  proposalId: Proposal["id"];
  transactionHash: Hash;
  chainId: number;
}) {
  // unique key for the tx.
  const key = `${chainId}-${transactionHash}`;
  const lastInvocationTime = lastInvocationTimes.get(key);
  
  // Check if on cooldown.
  if (lastInvocationTime && lastInvocationTime + 1000 * 15 > Date.now()) {
    console.debug(`polling ${transactionHash} on ${chainId} throttled`);
    return;
  }

  // Not invoked recently.
  lastInvocationTimes.set(key, Date.now());
  await _pollProposalTransactionAndUpdateIfResolved({
    proposalId,
    chainId,
    transactionHash,
  });
}

Asking because I'm not sure if all clients share the same server instance, so I don't know if lastInvocationTimes will always be correct? I'm using NextJS on vercel

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Throttling calls to a server function in NextJS