Postgresql Deadlock example using Pgx.Batch

db.sql

CREATE DATABASE testdb;

CREATE TABLE items (
    id SERIAL PRIMARY KEY,
    name TEXT,
    quantity INT
);

INSERT INTO items (name, quantity) VALUES ('Item1', 10);
INSERT INTO items (name, quantity) VALUES ('Item2', 20);

main.go

package main

import (
	"context"
	"fmt"
	"os"
	"sync"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"
)

func main() {
    connStr := "postgres://localhost/testdb"

    pool, err := pgxpool.New(context.Background(), connStr)
    if err != nil {
        fmt.Fprintf(os.Stderr, "Unable to connect to database: %v\n", err)
        os.Exit(1)
    }
    defer pool.Close()

    var wg sync.WaitGroup
	wg.Add(8)

	go updateItems(pool, &wg, 1, 2) 
	go updateItems(pool, &wg, 2, 1) 
	go updateItems(pool, &wg, 1, 2) 
	go updateItems(pool, &wg, 2, 1) 
	go updateItems(pool, &wg, 1, 2) 
	go updateItems(pool, &wg, 2, 1) 
	go updateItems(pool, &wg, 1, 2) 
	go updateItems(pool, &wg, 2, 1) 
	
	wg.Wait()
}

func updateItems(pool *pgxpool.Pool, wg *sync.WaitGroup, firstItemID, secondItemID int) {
    // Begin a batch of updates
    batch := &pgx.Batch{}
    batch.Queue(fmt.Sprintf("UPDATE items SET quantity = 11 WHERE id = %d", firstItemID))
    batch.Queue("SELECT pg_sleep(1)")
    batch.Queue(fmt.Sprintf("UPDATE items SET quantity = 21 WHERE id = %d", secondItemID))

    br := pool.SendBatch(context.Background(), batch)
    defer br.Close()

    _, err := br.Exec()
    if err != nil {
        fmt.Println("Error during batch execution:", err)
        return
    }
	wg.Done()
}