forked from mystiq/dex
126 lines
3.2 KiB
Go
126 lines
3.2 KiB
Go
// Copyright 2016 The Cockroach Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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// implied. See the License for the specific language governing
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// permissions and limitations under the License.
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//
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// Author: Spencer Kimball (spencer@cockroachlabs.com)
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package crdb
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import (
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"database/sql"
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"fmt"
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"sync"
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"testing"
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"github.com/cockroachdb/cockroach-go/testserver"
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)
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// TestExecuteTx verifies transaction retry using the classic
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// example of write skew in bank account balance transfers.
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func TestExecuteTx(t *testing.T) {
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db, stop := testserver.NewDBForTest(t)
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defer stop()
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initStmt := `
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CREATE DATABASE d;
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CREATE TABLE d.t (acct INT PRIMARY KEY, balance INT);
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INSERT INTO d.t (acct, balance) VALUES (1, 100), (2, 100);
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`
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if _, err := db.Exec(initStmt); err != nil {
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t.Fatal(err)
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}
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type queryI interface {
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Query(string, ...interface{}) (*sql.Rows, error)
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}
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getBalances := func(q queryI) (bal1, bal2 int, err error) {
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var rows *sql.Rows
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rows, err = q.Query(`SELECT balance FROM d.t WHERE acct IN (1, 2);`)
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if err != nil {
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return
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}
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defer rows.Close()
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balances := []*int{&bal1, &bal2}
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i := 0
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for ; rows.Next(); i += 1 {
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if err = rows.Scan(balances[i]); err != nil {
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return
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}
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}
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if i != 2 {
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err = fmt.Errorf("expected two balances; got %d", i)
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return
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}
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return
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}
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runTxn := func(wg *sync.WaitGroup, iter *int) <-chan error {
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errCh := make(chan error, 1)
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go func() {
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*iter = 0
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errCh <- ExecuteTx(db, func(tx *sql.Tx) error {
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*iter++
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bal1, bal2, err := getBalances(tx)
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if err != nil {
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return err
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}
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// If this is the first iteration, wait for the other tx to also read.
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if *iter == 1 {
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wg.Done()
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wg.Wait()
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}
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// Now, subtract from one account and give to the other.
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if bal1 > bal2 {
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if _, err := tx.Exec(`
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UPDATE d.t SET balance=balance-100 WHERE acct=1;
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UPDATE d.t SET balance=balance+100 WHERE acct=2;
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`); err != nil {
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return err
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}
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} else {
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if _, err := tx.Exec(`
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UPDATE d.t SET balance=balance+100 WHERE acct=1;
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UPDATE d.t SET balance=balance-100 WHERE acct=2;
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`); err != nil {
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return err
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}
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}
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return nil
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})
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}()
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return errCh
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}
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var wg sync.WaitGroup
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wg.Add(2)
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var iters1, iters2 int
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txn1Err := runTxn(&wg, &iters1)
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txn2Err := runTxn(&wg, &iters2)
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if err := <-txn1Err; err != nil {
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t.Errorf("expected success in txn1; got %s", err)
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}
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if err := <-txn2Err; err != nil {
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t.Errorf("expected success in txn2; got %s", err)
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}
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if iters1+iters2 <= 2 {
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t.Errorf("expected at least one retry between the competing transactions; "+
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"got txn1=%d, txn2=%d", iters1, iters2)
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}
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bal1, bal2, err := getBalances(db)
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if err != nil || bal1 != 100 || bal2 != 100 {
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t.Errorf("expected balances to be restored without error; "+
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"got acct1=%d, acct2=%d: %s", bal1, bal2, err)
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}
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}
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