I am using Node.js express for building REST api with postgres database using node-postgres package.
My question is whether I should use Client or Pool? I found this answer:
How can I choose between Client or Pool for node-postgres
but I don't understand what would be the use of Pool connection, since Nodejs is single-threaded and there won't be an attempt to use a single connection at the same time even if there are concurrent requests occurring.
Also by using a single connection, I can benefit from the prepared statements much more efficiently. I can prepare them at the initialization phase of my app, and then execute it whenever a request arrives.
Yes since Postgresql is still multithreaded.
When making a database request your process spends 0% CPU time executing code. Yes, you've read that right, zero.
The computer does not execute code in order to wait. Instead it sets up interrupt handlers and tells the hardware (ethernet card or wifi module) to send it an interrupt when there is data. Regardless of the number of requests you make to your database you still only have ONE ethernet card in your PC (well, some servers can have multiple and have increased bandwidth by trunking but I think you can see that the number of PCI cards you have does not have any relationship with the number of threads you are running - rather it is more related with the amount of $money you are willing to spend). Your hardware still basically sends all the requests out one bit at a time.
A traditional multi-threaded server therefore spends exactly the same amount of CPU time as node.js waiting for responses from the database: zero. Which means node.js improves efficiency by not needing to malloc a lot of RAM for each thread since node only has one thread.
Even when you are running your database on the same computer as your node process, communication with the database is not overly parallel. And the TCP/IP stack itself sort of serializes the communication. And while it does not go through the networking hardware the OS still schedules the responses using OS level events (instead of hardware interrupts).
So yes, it makes sense for your node.js process to make multiple parallel connections to the database even when node is singlethreaded - it is to allow the database to process requests in multiple database threads. You are making use of your database's multithreading instead of forcing your database to also use only one thread to process node's single connection.