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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 provides helpers for using CockroachDB in client
// applications.
package crdb
import (
"context"
"database/sql"
"fmt"
"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/stable/transactions.html.
//
// NOTE: the supplied exec closure should not have external side
// effects beyond changes to the database.
func ExecuteTx(ctx context.Context, db *sql.DB, txopts *sql.TxOptions, fn func(*sql.Tx) error) error {
// Start a transaction.
tx, err := db.BeginTx(ctx, txopts)
if err != nil {
return err
}
return ExecuteInTx(ctx, tx, func() error { return fn(tx) })
}
// Tx is used to permit clients to implement custom transaction logic.
type Tx interface {
ExecContext(context.Context, string, ...interface{}) (sql.Result, error)
Commit() error
Rollback() error
}
// ExecuteInTx runs fn inside tx which should already have begun.
// *WARNING*: Do not execute any statements on the supplied tx before calling this function.
// ExecuteInTx will only retry statements that are performed within the supplied
// closure (fn). Any statements performed on the tx before ExecuteInTx is invoked will *not*
// be re-run if the transaction needs to be retried.
func ExecuteInTx(ctx context.Context, tx Tx, fn func() error) (err error) {
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.ExecContext(ctx, "SAVEPOINT cockroach_restart"); err != nil {
return err
}
for {
released := false
err = fn()
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.ExecContext(ctx, "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.ExecContext(ctx, "ROLLBACK TO SAVEPOINT cockroach_restart"); err != nil {
// ROLLBACK TO SAVEPOINT failed. If it failed with a lib/pq error, we want
// to pass this error to the client, but also include the original error
// message and code. So, we'll do some surgery on lib/pq errors in
// particular.
// If it failed with any other error (e.g. the "driver: bad connection" is
// untyped), we overwrite the error.
msgPattern := "restarting txn failed. ROLLBACK TO SAVEPOINT encountered error: %s. " +
"Original error (code: %s): %s."
if rollbackPQErr, ok := err.(*pq.Error); ok {
rollbackPQErr.Message = fmt.Sprintf(msgPattern, rollbackPQErr, pqErr.Code, pqErr)
return rollbackPQErr
}
return fmt.Errorf(msgPattern, err, pqErr.Code, pqErr)
}
}
}
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