How to avoid memory leak when using pub sub to call function?

I stuck on performance issue when using pubsub to triggers the function.

//this will call on index.ts
export function downloadService() {
  // References an existing subscription
  const subscription = pubsub.subscription("DOWNLOAD-sub");

  // Create an event handler to handle messages
  // let messageCount = 0;
  const messageHandler = async (message : any) => {
    console.log(`Received message ${message.id}:`);
    console.log(`\tData: ${message.data}`);
    console.log(`\tAttributes: ${message.attributes.type}`);

    // "Ack" (acknowledge receipt of) the message
    message.ack();
    await exportExcel(message);//my function
    // messageCount += 1;
  };


  // Listen for new messages until timeout is hit
  subscription.on("message", messageHandler);
} 

async function exportExcel(message : any) {
 //get data from database
 const movies = await Sales.findAll({
    attributes: [
      "SALES_STORE",
      "SALES_CTRNO",
      "SALES_TRANSNO",
      "SALES_STATUS",
    ],
    raw: true,
  });
  ... processing to excel// 800k rows
  ... bucket.upload to gcs

}

The function above is working fine if I trigger ONLY one pubsub message. However, the function will hit memory leak issue or database connection timeout issue if I trigger many pubsub message in short period of time.

The problem I found is, first processing havent finish yet but others request from pubsub will straight to call function again and process at the same time.

I have no idea how to resolve this but I was thinking implement the queue worker or google cloud task will solve the problem?