diff --git a/contrib/cppkafka b/contrib/cppkafka
index 9b184d881c1..860c90e92ee 160000
--- a/contrib/cppkafka
+++ b/contrib/cppkafka
@@ -1 +1 @@
-Subproject commit 9b184d881c15cc50784b28688c7c99d3d764db24
+Subproject commit 860c90e92eee6690aa74a2ca7b7c5c6930dffecd
diff --git a/contrib/librdkafka b/contrib/librdkafka
index 51ae5f5fd8b..363dcad5a23 160000
--- a/contrib/librdkafka
+++ b/contrib/librdkafka
@@ -1 +1 @@
-Subproject commit 51ae5f5fd8b742e56f47a8bb0136344868818285
+Subproject commit 363dcad5a23dc29381cc626620e68ae418b3af19
diff --git a/dbms/src/Storages/IStorage.h b/dbms/src/Storages/IStorage.h
index 8a362d33aae..6d52afe5314 100644
--- a/dbms/src/Storages/IStorage.h
+++ b/dbms/src/Storages/IStorage.h
@@ -347,7 +347,8 @@ private:
     mutable RWLock alter_intention_lock = RWLockImpl::create();
 
     /// It is taken for share for the entire INSERT query and the entire merge of the parts (for MergeTree).
-    /// ALTER queries acquire an exclusive lock to ensure
+    /// ALTER COLUMN queries acquire an exclusive lock to ensure that no new parts with the old structure
+    /// are added to the table and thus the set of parts to modify doesn't change.
     mutable RWLock new_data_structure_lock = RWLockImpl::create();
 
     /// Lock for the table column structure (names, types, etc.) and data path.