我有配置池。这里用min和max属性配置了什么？

require('dotenv').config();
const config = {
    client: 'pg',
    connection: {
      host:     process.env.POSTGRES_HOST || 'localhost',
      database: process.env.POSTGRES_DB || 'vo2',
      user:     process.env.POSTGRES_USER || 'postgres',
      password: process.env.POSTGRES_PASSWORD || 'windofchange'
    },
    pool: { min: 0, max: 10 },
    migrations: { directory: './db/migrations' }
};
module.exports = config;