Set a transaction isolation level for MySQL connections (#1156)

* Set transaction isolation in connections

* Revert load_map.go change

* Var rename

* Restore comment

doc/requirements-and-limitations.md

@@ -20,6 +20,8 @@ The `SUPER` privilege is required for `STOP SLAVE`, `START SLAVE` operations. Th
 - Switching your `binlog_format` to `ROW`, in the case where it is _not_ `ROW` and you explicitly specified `--switch-to-rbr`
   - If your replication is already in RBR (`binlog_format=ROW`) you can specify `--assume-rbr` to avoid the `STOP SLAVE/START SLAVE` operations, hence no need for `SUPER`.
 
+- `gh-ost` uses the `REPEATABLE_READ` transaction isolation level for all MySQL connections, regardless of the server default.
+
 - Running `--test-on-replica`: before the cut-over phase, `gh-ost` stops replication so that you can compare the two tables and satisfy that the migration is sound.
 
 ### Limitations

go/cmd/gh-ost/main.go

@@ -181,7 +181,7 @@ func main() {
 	}
 
 	if migrationContext.AlterStatement == "" {
-		log.Fatalf("--alter must be provided and statement must not be empty")
+		log.Fatal("--alter must be provided and statement must not be empty")
 	}
 	parser := sql.NewParserFromAlterStatement(migrationContext.AlterStatement)
 	migrationContext.AlterStatementOptions = parser.GetAlterStatementOptions()
@@ -190,7 +190,7 @@ func main() {
 		if parser.HasExplicitSchema() {
 			migrationContext.DatabaseName = parser.GetExplicitSchema()
 		} else {
-			log.Fatalf("--database must be provided and database name must not be empty, or --alter must specify database name")
+			log.Fatal("--database must be provided and database name must not be empty, or --alter must specify database name")
 		}
 	}
 
@@ -202,48 +202,48 @@ func main() {
 		if parser.HasExplicitTable() {
 			migrationContext.OriginalTableName = parser.GetExplicitTable()
 		} else {
-			log.Fatalf("--table must be provided and table name must not be empty, or --alter must specify table name")
+			log.Fatal("--table must be provided and table name must not be empty, or --alter must specify table name")
 		}
 	}
 	migrationContext.Noop = !(*executeFlag)
 	if migrationContext.AllowedRunningOnMaster && migrationContext.TestOnReplica {
-		migrationContext.Log.Fatalf("--allow-on-master and --test-on-replica are mutually exclusive")
+		migrationContext.Log.Fatal("--allow-on-master and --test-on-replica are mutually exclusive")
 	}
 	if migrationContext.AllowedRunningOnMaster && migrationContext.MigrateOnReplica {
-		migrationContext.Log.Fatalf("--allow-on-master and --migrate-on-replica are mutually exclusive")
+		migrationContext.Log.Fatal("--allow-on-master and --migrate-on-replica are mutually exclusive")
 	}
 	if migrationContext.MigrateOnReplica && migrationContext.TestOnReplica {
-		migrationContext.Log.Fatalf("--migrate-on-replica and --test-on-replica are mutually exclusive")
+		migrationContext.Log.Fatal("--migrate-on-replica and --test-on-replica are mutually exclusive")
 	}
 	if migrationContext.SwitchToRowBinlogFormat && migrationContext.AssumeRBR {
-		migrationContext.Log.Fatalf("--switch-to-rbr and --assume-rbr are mutually exclusive")
+		migrationContext.Log.Fatal("--switch-to-rbr and --assume-rbr are mutually exclusive")
 	}
 	if migrationContext.TestOnReplicaSkipReplicaStop {
 		if !migrationContext.TestOnReplica {
-			migrationContext.Log.Fatalf("--test-on-replica-skip-replica-stop requires --test-on-replica to be enabled")
+			migrationContext.Log.Fatal("--test-on-replica-skip-replica-stop requires --test-on-replica to be enabled")
 		}
 		migrationContext.Log.Warning("--test-on-replica-skip-replica-stop enabled. We will not stop replication before cut-over. Ensure you have a plugin that does this.")
 	}
 	if migrationContext.CliMasterUser != "" && migrationContext.AssumeMasterHostname == "" {
-		migrationContext.Log.Fatalf("--master-user requires --assume-master-host")
+		migrationContext.Log.Fatal("--master-user requires --assume-master-host")
 	}
 	if migrationContext.CliMasterPassword != "" && migrationContext.AssumeMasterHostname == "" {
-		migrationContext.Log.Fatalf("--master-password requires --assume-master-host")
+		migrationContext.Log.Fatal("--master-password requires --assume-master-host")
 	}
 	if migrationContext.TLSCACertificate != "" && !migrationContext.UseTLS {
-		migrationContext.Log.Fatalf("--ssl-ca requires --ssl")
+		migrationContext.Log.Fatal("--ssl-ca requires --ssl")
 	}
 	if migrationContext.TLSCertificate != "" && !migrationContext.UseTLS {
-		migrationContext.Log.Fatalf("--ssl-cert requires --ssl")
+		migrationContext.Log.Fatal("--ssl-cert requires --ssl")
 	}
 	if migrationContext.TLSKey != "" && !migrationContext.UseTLS {
-		migrationContext.Log.Fatalf("--ssl-key requires --ssl")
+		migrationContext.Log.Fatal("--ssl-key requires --ssl")
 	}
 	if migrationContext.TLSAllowInsecure && !migrationContext.UseTLS {
-		migrationContext.Log.Fatalf("--ssl-allow-insecure requires --ssl")
+		migrationContext.Log.Fatal("--ssl-allow-insecure requires --ssl")
 	}
 	if *replicationLagQuery != "" {
-		migrationContext.Log.Warningf("--replication-lag-query is deprecated")
+		migrationContext.Log.Warning("--replication-lag-query is deprecated")
 	}
 
 	switch *cutOver {

go/mysql/connection.go

@@ -1,5 +1,5 @@
 /*
-   Copyright 2016 GitHub Inc.
+   Copyright 2022 GitHub Inc.
 	 See https://github.com/github/gh-ost/blob/master/LICENSE
 */
 
@@ -12,11 +12,13 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net"
+	"strings"
 
 	"github.com/go-sql-driver/mysql"
 )
 
 const (
+	transactionIsolation = "REPEATABLE-READ"
 	TLS_CONFIG_KEY       = "ghost"
 )
 
@@ -112,12 +114,23 @@ func (this *ConnectionConfig) GetDBUri(databaseName string) string {
 		// Wrap IPv6 literals in square brackets
 		hostname = fmt.Sprintf("[%s]", hostname)
 	}
-	interpolateParams := true
+
 	// go-mysql-driver defaults to false if tls param is not provided; explicitly setting here to
 	// simplify construction of the DSN below.
 	tlsOption := "false"
 	if this.tlsConfig != nil {
 		tlsOption = TLS_CONFIG_KEY
 	}
-	return fmt.Sprintf("%s:%s@tcp(%s:%d)/%s?timeout=%fs&readTimeout=%fs&writeTimeout=%fs&interpolateParams=%t&autocommit=true&charset=utf8mb4,utf8,latin1&tls=%s", this.User, this.Password, hostname, this.Key.Port, databaseName, this.Timeout, this.Timeout, this.Timeout, interpolateParams, tlsOption)
+	connectionParams := []string{
+		"autocommit=true",
+		"charset=utf8mb4,utf8,latin1",
+		"interpolateParams=true",
+		fmt.Sprintf("tls=%s", tlsOption),
+		fmt.Sprintf("transaction_isolation=%q", transactionIsolation),
+		fmt.Sprintf("timeout=%fs", this.Timeout),
+		fmt.Sprintf("readTimeout=%fs", this.Timeout),
+		fmt.Sprintf("writeTimeout=%fs", this.Timeout),
+	}
+
+	return fmt.Sprintf("%s:%s@tcp(%s:%d)/%s?%s", this.User, this.Password, hostname, this.Key.Port, databaseName, strings.Join(connectionParams, "&"))
 }

go/mysql/connection_test.go

@@ -1,5 +1,5 @@
 /*
-   Copyright 2016 GitHub Inc.
+   Copyright 2022 GitHub Inc.
 	 See https://github.com/github/gh-ost/blob/master/LICENSE
 */
 
@@ -67,9 +67,10 @@ func TestGetDBUri(t *testing.T) {
 	c.Key = InstanceKey{Hostname: "myhost", Port: 3306}
 	c.User = "gromit"
 	c.Password = "penguin"
+	c.Timeout = 1.2345
 
 	uri := c.GetDBUri("test")
-	test.S(t).ExpectEquals(uri, "gromit:penguin@tcp(myhost:3306)/test?timeout=0.000000s&readTimeout=0.000000s&writeTimeout=0.000000s&interpolateParams=true&autocommit=true&charset=utf8mb4,utf8,latin1&tls=false")
+	test.S(t).ExpectEquals(uri, `gromit:penguin@tcp(myhost:3306)/test?autocommit=true&charset=utf8mb4,utf8,latin1&interpolateParams=true&tls=false&transaction_isolation="REPEATABLE-READ"&timeout=1.234500s&readTimeout=1.234500s&writeTimeout=1.234500s`)
 }
 
 func TestGetDBUriWithTLSSetup(t *testing.T) {
@@ -77,8 +78,9 @@ func TestGetDBUriWithTLSSetup(t *testing.T) {
 	c.Key = InstanceKey{Hostname: "myhost", Port: 3306}
 	c.User = "gromit"
 	c.Password = "penguin"
+	c.Timeout = 1.2345
 	c.tlsConfig = &tls.Config{}
 
 	uri := c.GetDBUri("test")
-	test.S(t).ExpectEquals(uri, "gromit:penguin@tcp(myhost:3306)/test?timeout=0.000000s&readTimeout=0.000000s&writeTimeout=0.000000s&interpolateParams=true&autocommit=true&charset=utf8mb4,utf8,latin1&tls=ghost")
+	test.S(t).ExpectEquals(uri, `gromit:penguin@tcp(myhost:3306)/test?autocommit=true&charset=utf8mb4,utf8,latin1&interpolateParams=true&tls=ghost&transaction_isolation="REPEATABLE-READ"&timeout=1.234500s&readTimeout=1.234500s&writeTimeout=1.234500s`)
 }