I don't understand local development

import { AsyncLocalStorage } from 'node:async_hooks'
import { Client } from 'pg'
import { drizzle, type NodePgDatabase } from 'drizzle-orm/node-postgres'
import * as schema from './schema'

export type NodeDatabase = NodePgDatabase<typeof schema>

const dbStorage = new AsyncLocalStorage<NodeDatabase>()

function createDatabaseConnection(dbConnectionUrl: string) {
  const client = new Client({ connectionString: dbConnectionUrl })
  const db = drizzle(client, { schema })
  return { db, client }
}

export async function runWithDb<T>(
  dbConnectionUrl: string,
  callback: () => Promise<T>,
): Promise<T> {
  const existing = dbStorage.getStore()
  if (existing) return callback()

  const { db, client } = createDatabaseConnection(dbConnectionUrl)
  await client.connect()

  try {
    return await dbStorage.run(db, callback)
  } finally {
    await client.end()
  }
}

export function getDb(): NodeDatabase {
  const db = dbStorage.getStore()
  if (!db) throw new Error('Database not available — not in a request context')
  return db
}