MDEV-10314.assert.patch

diff --git a/sql/wsrep_mysqld.cc b/sql/wsrep_mysqld.cc
index 11c1bef..04ba4aa 100644
--- a/sql/wsrep_mysqld.cc
+++ b/sql/wsrep_mysqld.cc
@@ -995,6 +995,12 @@ bool wsrep_sync_wait (THD* thd, uint mask)
       return true;
     }
   }
+  /* SELECT must have waited for wsrep_sync_wait=1. */
+  else if ((thd->lex->sql_command == SQLCOM_SELECT) &&
+           (thd->variables.wsrep_sync_wait & WSREP_SYNC_WAIT_BEFORE_READ))
+  {
+    DBUG_ASSERT(false);
+  }
 
   return false;
 }