fix: reduce persistence lag and retry audit deadlocks

server/db/mysql/tenant_security_audit_test.go

@@ -3,9 +3,13 @@
 package mysql
 
 import (
+	"errors"
 	"os"
 	"strings"
 	"testing"
+	"time"
+
+	mysqldriver "github.com/go-sql-driver/mysql"
 )
 
 func TestLoginAuditQueriesAreTenantScoped(t *testing.T) {
@@ -24,3 +28,48 @@ func TestLoginAuditQueriesAreTenantScoped(t *testing.T) {
 		}
 	}
 }
+
+func TestRetryMySQLDeadlockEventuallySucceeds(t *testing.T) {
+	calls := 0
+	var delays []time.Duration
+	err := retryMySQLDeadlock(func() error {
+		calls++
+		if calls < 3 {
+			return &mysqldriver.MySQLError{Number: 1213, SQLState: [5]byte{'4', '0', '0', '0', '1'}}
+		}
+		return nil
+	}, func(delay time.Duration) { delays = append(delays, delay) })
+	if err != nil {
+		t.Fatal(err)
+	}
+	if calls != 3 {
+		t.Fatalf("operation calls=%d want=3", calls)
+	}
+	want := []time.Duration{25 * time.Millisecond, 50 * time.Millisecond}
+	if len(delays) != len(want) || delays[0] != want[0] || delays[1] != want[1] {
+		t.Fatalf("retry delays=%v want=%v", delays, want)
+	}
+}
+
+func TestRetryMySQLDeadlockStopsOnNonRetryableError(t *testing.T) {
+	want := errors.New("invalid update")
+	calls := 0
+	err := retryMySQLDeadlock(func() error {
+		calls++
+		return want
+	}, func(time.Duration) { t.Fatal("non-retryable error must not sleep") })
+	if !errors.Is(err, want) || calls != 1 {
+		t.Fatalf("err=%v calls=%d want=%v/1", err, calls, want)
+	}
+}
+
+func TestRetryMySQLDeadlockStopsAfterFourAttempts(t *testing.T) {
+	calls := 0
+	err := retryMySQLDeadlock(func() error {
+		calls++
+		return &mysqldriver.MySQLError{Number: 1205}
+	}, func(time.Duration) {})
+	if err == nil || calls != 4 {
+		t.Fatalf("err=%v calls=%d want non-nil/4", err, calls)
+	}
+}