*: revendor

vendor/github.com/cockroachdb/cockroach-go/crdb/tx.go

@@ -0,0 +1,95 @@
+// 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.
+//
+// Author: Andrei Matei (andrei@cockroachlabs.com)
+
+// Package crdb provides helpers for using CockroachDB in client
+// applications.
+package crdb
+
+import (
+	"database/sql"
+
+	"github.com/lib/pq"
+)
+
+// AmbiguousCommitError represents an error that left a transaction in an
+// ambiguous state: unclear if it committed or not.
+type AmbiguousCommitError struct {
+	error
+}
+
+// ExecuteTx runs fn inside a transaction and retries it as needed.
+// On non-retryable failures, the transaction is aborted and rolled
+// back; on success, the transaction is committed.
+// There are cases where the state of a transaction is inherently ambiguous: if
+// we err on RELEASE with a communication error it's unclear if the transaction
+// has been committed or not (similar to erroring on COMMIT in other databases).
+// In that case, we return AmbiguousCommitError.
+//
+// For more information about CockroachDB's transaction model see
+// https://cockroachlabs.com/docs/transactions.html.
+//
+// NOTE: the supplied exec closure should not have external side
+// effects beyond changes to the database.
+func ExecuteTx(db *sql.DB, fn func(*sql.Tx) error) (err error) {
+	// Start a transaction.
+	var tx *sql.Tx
+	tx, err = db.Begin()
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if err == nil {
+			// Ignore commit errors. The tx has already been committed by RELEASE.
+			_ = tx.Commit()
+		} else {
+			// We always need to execute a Rollback() so sql.DB releases the
+			// connection.
+			_ = tx.Rollback()
+		}
+	}()
+	// Specify that we intend to retry this txn in case of CockroachDB retryable
+	// errors.
+	if _, err = tx.Exec("SAVEPOINT cockroach_restart"); err != nil {
+		return err
+	}
+
+	for {
+		released := false
+		err = fn(tx)
+		if err == nil {
+			// RELEASE acts like COMMIT in CockroachDB. We use it since it gives us an
+			// opportunity to react to retryable errors, whereas tx.Commit() doesn't.
+			released = true
+			if _, err = tx.Exec("RELEASE SAVEPOINT cockroach_restart"); err == nil {
+				return nil
+			}
+		}
+		// We got an error; let's see if it's a retryable one and, if so, restart. We look
+		// for either the standard PG errcode SerializationFailureError:40001 or the Cockroach extension
+		// errcode RetriableError:CR000. The Cockroach extension has been removed server-side, but support
+		// for it has been left here for now to maintain backwards compatibility.
+		pqErr, ok := err.(*pq.Error)
+		if retryable := ok && (pqErr.Code == "CR000" || pqErr.Code == "40001"); !retryable {
+			if released {
+				err = &AmbiguousCommitError{err}
+			}
+			return err
+		}
+		if _, err = tx.Exec("ROLLBACK TO SAVEPOINT cockroach_restart"); err != nil {
+			return err
+		}
+	}
+}

vendor/github.com/cockroachdb/cockroach-go/crdb/tx_test.go

@@ -0,0 +1,125 @@
+// 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.
+//
+// Author: Spencer Kimball (spencer@cockroachlabs.com)
+
+package crdb
+
+import (
+	"database/sql"
+	"fmt"
+	"sync"
+	"testing"
+
+	"github.com/cockroachdb/cockroach-go/testserver"
+)
+
+// 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)
+	}
+}