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