Add --transaction-isolation flag

doc/command-line-flags.md

@@ -294,6 +294,10 @@ Defaults to 1000 (1 second). Configures the HTTP throttler check timeout in mill
 
 Makes the _old_ table include a timestamp value. The _old_ table is what the original table is renamed to at the end of a successful migration. For example, if the table is `gh_ost_test`, then the _old_ table would normally be `_gh_ost_test_del`. With `--timestamp-old-table` it would be, for example, `_gh_ost_test_20170221103147_del`.
 
+### transaction-isolation
+
+Defaults to `REPEATABLE-READ`. Configures the session-level transaction isolation level used for applier and inspector connections. Possible values: `REPEATABLE-READ` or `READ-COMMITTED`.
+
 ### tungsten
 
 See [`tungsten`](cheatsheet.md#tungsten) on the cheatsheet.

go/base/context.go

@@ -6,6 +6,7 @@
 package base
 
 import (
+	"errors"
 	"fmt"
 	"math"
 	"os"
@@ -293,13 +294,16 @@ func NewMigrationContext() *MigrationContext {
 	}
 }
 
-func (this *MigrationContext) SetConnectionConfig(storageEngine string) error {
-	var transactionIsolation string
+func (this *MigrationContext) SetConnectionConfig(storageEngine, transactionIsolation string) error {
 	switch storageEngine {
 	case "rocksdb":
 		transactionIsolation = "READ-COMMITTED"
 	default:
-		transactionIsolation = "REPEATABLE-READ"
+		switch transactionIsolation {
+		case "READ-COMMITTED", "REPEATABLE-READ":
+		default:
+			return errors.New("unsupported transaction isolation level")
+		}
 	}
 	this.InspectorConnectionConfig.TransactionIsolation = transactionIsolation
 	this.ApplierConnectionConfig.TransactionIsolation = transactionIsolation

go/cmd/gh-ost/main.go

@@ -108,6 +108,7 @@ func main() {
 	dmlBatchSize := flag.Int64("dml-batch-size", 10, "batch size for DML events to apply in a single transaction (range 1-100)")
 	defaultRetries := flag.Int64("default-retries", 60, "Default number of retries for various operations before panicking")
 	cutOverLockTimeoutSeconds := flag.Int64("cut-over-lock-timeout-seconds", 3, "Max number of seconds to hold locks on tables while attempting to cut-over (retry attempted when lock exceeds timeout)")
+	transactionIsolation := flag.String("transaction-isolation", "REPEATABLE-READ", "transaction isolation level to be used by the applier and inspector. Possible values: REPEATABLE-READ or READ-COMMITTED")
 	niceRatio := flag.Float64("nice-ratio", 0, "force being 'nice', imply sleep time per chunk time; range: [0.0..100.0]. Example values: 0 is aggressive. 1: for every 1ms spent copying rows, sleep additional 1ms (effectively doubling runtime); 0.7: for every 10ms spend in a rowcopy chunk, spend 7ms sleeping immediately after")
 
 	maxLagMillis := flag.Int64("max-lag-millis", 1500, "replication lag at which to throttle operation")
@@ -188,7 +189,7 @@ func main() {
 		migrationContext.Log.SetLevel(log.ERROR)
 	}
 
-	if err := migrationContext.SetConnectionConfig(*storageEngine); err != nil {
+	if err := migrationContext.SetConnectionConfig(*storageEngine, *transactionIsolation); err != nil {
 		migrationContext.Log.Fatale(err)
 	}