diff --git a/src/Databases/IDatabase.h b/src/Databases/IDatabase.h
index 5b3003f36b4..b80e73be108 100644
--- a/src/Databases/IDatabase.h
+++ b/src/Databases/IDatabase.h
@@ -161,6 +161,7 @@ public:
     /// Is the database empty.
     virtual bool empty() const = 0;
 
+    /// Submit query to log. Currently used by DatabaseReplicated engine only.
     virtual void propose(const ASTPtr & /*query*/) {
         throw Exception(getEngineName() + ": propose() is not supported", ErrorCodes::NOT_IMPLEMENTED);
     }