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// Copyright 2016 The Cockroach Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.
package crdb
import (
"context"
"database/sql"
"fmt"
"sync"
"testing"
"github.com/cockroachdb/cockroach-go/testserver"
)
func TestExecuteTx(t *testing.T) {
testExecuteTxInner(t, ExecuteTx)
}
func TestExecuteInTx(t *testing.T) {
executeTx := func(
ctx context.Context,
db *sql.DB,
opts *sql.TxOptions,
fn func(*sql.Tx) error,
) error {
tx, err := db.BeginTx(ctx, opts)
if err != nil {
return err
}
return ExecuteInTx(ctx, tx, func() error { return fn(tx) })
}
testExecuteTxInner(t, executeTx)
}
// TestExecuteTx verifies transaction retry using the classic
// example of write skew in bank account balance transfers.
func testExecuteTxInner(
t *testing.T,
executeTxFn func(
context.Context,
*sql.DB,
*sql.TxOptions,
func(*sql.Tx) error,
) error,
) {
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++ {
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 <- executeTxFn(context.Background(), db, nil, 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)
}
}
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