cannot cancel postgres query outside of transaction

check_cancel.go

package main

import (
	"database/sql"
	"flag"
	"log"
	"time"

	_ "github.com/lib/pq"
)

func withTx(db *sql.DB, cancelAfter time.Duration, result chan string) {
	tx, err := db.Begin()
	if err != nil {
		panic(err)
	}

	// approx ~45s on a 3.1Ghz i7
	SQL := `select sum(length(replace(generate_series::bigint::bit(64)::text,'0','')))
	 from generate_series(0,10e6);`

	nbits := ""
	time.AfterFunc(cancelAfter, func() {
		result <- "timeout!"
		tx.Rollback()
	})
	err = tx.QueryRow(SQL).Scan(&nbits)
	if err != nil {
		panic(err)
	}
	result <- nbits
	tx.Commit()
}

func withoutTx(db *sql.DB, cancelAfter time.Duration, result chan string) {
	// approx ~45s on a 3.1Ghz i7
	SQL := `select sum(length(replace(generate_series::bigint::bit(64)::text,'0','')))
	 from generate_series(0,10e6);`

	nbits := ""
	time.AfterFunc(cancelAfter, func() {
		result <- "timeout!"
		db.Close()
	})
	err := db.QueryRow(SQL).Scan(&nbits)
	if err != nil {
		panic(err)
	}
	result <- nbits
}

func main() {
	useTx := flag.Bool("tx", false, "try in a transaction")
	cancelAfter := flag.Duration("w", time.Second*2, "how long to wait for response")
	connstr := flag.String("db", "sslmode=disable", "postgres connection string")
	flag.Parse()

	db, _ := sql.Open("postgres", *connstr)

	result := make(chan string)
	go func() {
		res := <-result
		log.Println("RESULT: ", res)
	}()

	if *useTx {
		go withTx(db, *cancelAfter, result)
	} else {
		go withoutTx(db, *cancelAfter, result)
	}

	log.Println("sleeping 1 min - watch CPU for DB process")
	time.Sleep(time.Minute)
}