func TestRunServer(t *testing.T) {
db, stop := testserver.NewDBForTest(t)
defer stop()
_, err := db.Exec("SELECT 1")
if err != nil {
t.Fatal(err)
}
}
func initTestDB(t *testing.T) (*sql.DB, func()) {
db, stop := testserver.NewDBForTest(t)
if err := initSchema(db); err != nil {
stop()
t.Fatal(err)
}
return db, stop
}
// TestExecuteTx verifies transaction retry using the classic
// example of write skew in bank account balance transfers.
func TestExecuteTx(t *testing.T) {
db, stop := testserver.NewDBForTest(t)
defer stop()
initStmt := `
CREATE DATABASE d;
CREATE TABLE d.t (acct INT PRIMARY KEY, balance INT);
INSERT INTO d.t (acct, balance) VALUES (1, 100), (2, 100);
`
if _, err := db.Exec(initStmt); err != nil {
t.Fatal(err)
}
type queryI interface {
Query(string, ...interface{}) (*sql.Rows, error)
}
getBalances := func(q queryI) (bal1, bal2 int, err error) {
var rows *sql.Rows
rows, err = q.Query(`SELECT balance FROM d.t WHERE acct IN (1, 2);`)
if err != nil {
return
}
defer rows.Close()
balances := []*int{&bal1, &bal2}
i := 0
for ; rows.Next(); i += 1 {
if err = rows.Scan(balances[i]); err != nil {
return
}
}
if i != 2 {
err = fmt.Errorf("expected two balances; got %d", i)
return
}
return
}
runTxn := func(wg *sync.WaitGroup, iter *int) <-chan error {
errCh := make(chan error, 1)
go func() {
*iter = 0
errCh <- ExecuteTx(db, func(tx *sql.Tx) error {
*iter++
bal1, bal2, err := getBalances(tx)
if err != nil {
return err
}
// If this is the first iteration, wait for the other tx to also read.
if *iter == 1 {
wg.Done()
wg.Wait()
}
// Now, subtract from one account and give to the other.
if bal1 > bal2 {
if _, err := tx.Exec(`
UPDATE d.t SET balance=balance-100 WHERE acct=1;
UPDATE d.t SET balance=balance+100 WHERE acct=2;
`); err != nil {
return err
}
} else {
if _, err := tx.Exec(`
UPDATE d.t SET balance=balance+100 WHERE acct=1;
UPDATE d.t SET balance=balance-100 WHERE acct=2;
`); err != nil {
return err
}
}
return nil
})
}()
return errCh
}
var wg sync.WaitGroup
wg.Add(2)
var iters1, iters2 int
txn1Err := runTxn(&wg, &iters1)
txn2Err := runTxn(&wg, &iters2)
if err := <-txn1Err; err != nil {
t.Errorf("expected success in txn1; got %s", err)
}
if err := <-txn2Err; err != nil {
t.Errorf("expected success in txn2; got %s", err)
}
if iters1+iters2 <= 2 {
t.Errorf("expected at least one retry between the competing transactions; "+
"got txn1=%d, txn2=%d", iters1, iters2)
}
bal1, bal2, err := getBalances(db)
if err != nil || bal1 != 100 || bal2 != 100 {
t.Errorf("expected balances to be restored without error; "+
"got acct1=%d, acct2=%d: %s", bal1, bal2, err)
}
}