feat(query): add RaftReadBarrier

pkg/util/query/query.go

@@ -3,12 +3,15 @@
 package query
 
 import (
+	"fmt"
 	"strings"
 
+	"github.com/gocql/gocql"
 	"github.com/pkg/errors"
 	"github.com/scylladb/go-set/strset"
 	"github.com/scylladb/gocqlx/v2"
 	"github.com/scylladb/gocqlx/v2/qb"
+	"github.com/scylladb/scylla-manager/v3/pkg/util/uuid"
 )
 
 // GetAllViews returns set of all views present in cluster.
@@ -78,3 +81,30 @@ func DescribeSchemaWithInternals(session gocqlx.Session) (DescribedSchema, error
 	}
 	return schema, nil
 }
+
+// RaftReadBarrier performs read barrier on a random node to which session is connected to.
+// When used with single host session, it can be used to ensure that given node
+// has already applied all raft commands present in the raft log.
+func RaftReadBarrier(session gocqlx.Session) error {
+	// As this functionality is not available from Scylla API,
+	// SM uses the workaround described in https://github.com/scylladb/scylladb/issues/19213.
+	// Read barrier is performed before any schema change, so it's enough to try to apply
+	// some dummy schema changing CQL statement.
+	// In order to avoid misleading errors, it's good to use the IF EXISTS clause.
+	// Still, it might happen that SM does not have the permissions to perform dummy schema change.
+	// As described in the issue, this type of error still results in performing read barrier,
+	// so SM should treat it as if everything went fine.
+	// TODO: swap workaround with proper API call when mentioned issue is fixed.
+	// nolint: godox
+	tmpName := strings.ReplaceAll(uuid.NewTime().String(), "-", "")
+	readBarrierStmt := fmt.Sprintf("DROP TABLE IF EXISTS %q.%q", tmpName, tmpName)
+	if err := session.ExecStmt(readBarrierStmt); err != nil && !isGocqlUnauthorizedError(err) {
+		return errors.Wrap(err, "exec dummy schema change")
+	}
+	return nil
+}
+
+func isGocqlUnauthorizedError(err error) bool {
+	var reqErr gocql.RequestError
+	return errors.As(err, &reqErr) && reqErr.Code() == gocql.ErrCodeUnauthorized
+}