why is my first query slow but then it is fast?

Question

If I go to my site I get data from database. First Load is slow and takes 1-2 seconds. But then it is fast like 10ms. Why is the first connection slow? It is only when I use cassandra driver.

const http = require('http');

require('dotenv').config();

const { Client } = require('cassandra-driver');

const express = require('express');

const app = express();

const PORT = process.env.PORT;

const routes = require('./src/routes/index');

const client = new Client({
  cloud: {
    secureConnectBundle: "secure-connect-weinf.zip",
  },
  keyspace: 'wf_db',
  credentials: {
    username: "username",
    password: "password",
  },
});

const cors = require('cors');

app.use(cors());

app.use(express.json());

app.get('/', async (req, res) => {
  await client.connect();
  const rs = await client.execute("SELECT * FROM employ_by_id;");
  console.log(rs);
  return res.json({
    message: 'Hello'
  })
});

const server = http.createServer(app);

server.listen(PORT, () => {
  console.log(`Server listen on port ${PORT}`)
});

Answer 1

Your code is connecting (creating the TCP connections) the first time:

app.get('/', async (req, res) => {
  await client.connect(); // <- this should be avoiding in the serve path
  const rs = await client.execute("SELECT * FROM employ_by_id;");
  console.log(rs);
  return res.json({
    message: 'Hello'
  })
});

To mitigate this, you can create the connections beforehard:

app.get('/', async (req, res) => {
  const rs = await client.execute("SELECT * FROM employ_by_id;");
  console.log(rs);
  return res.json({
    message: 'Hello'
  })
});

const server = http.createServer(app);
client.connect(err => {
  //TODO: Handle err
  // ...
  // Now that I'm connected to my DB, I can start serving requests
  server.listen(PORT, () => {
    console.log(`Server listen on port ${PORT}`)
  });
});