diff --git a/dbms/src/DataStreams/ExpressionBlockInputStream.cpp b/dbms/src/DataStreams/ExpressionBlockInputStream.cpp
index 4e709c503be..51adc462ef6 100644
--- a/dbms/src/DataStreams/ExpressionBlockInputStream.cpp
+++ b/dbms/src/DataStreams/ExpressionBlockInputStream.cpp
@@ -8,7 +8,6 @@ namespace DB
 ExpressionBlockInputStream::ExpressionBlockInputStream(const BlockInputStreamPtr & input, const ExpressionActionsPtr & expression_)
     : expression(expression_)
 {
-    std::cerr << "expression: " << expression->dumpActions();
     children.push_back(input);
     cached_header = children.back()->getHeader();
     expression->execute(cached_header, true);
diff --git a/dbms/src/Storages/MergeTree/IMergeTreeDataPart.cpp b/dbms/src/Storages/MergeTree/IMergeTreeDataPart.cpp
index b555a75c140..79c8584f5fd 100644
--- a/dbms/src/Storages/MergeTree/IMergeTreeDataPart.cpp
+++ b/dbms/src/Storages/MergeTree/IMergeTreeDataPart.cpp
@@ -224,6 +224,7 @@ time_t IMergeTreeDataPart::getMaxTime() const
 void IMergeTreeDataPart::setColumns(const NamesAndTypesList & columns_)
 {
     columns = columns_;
+    sample_block.clear();
     for (const auto & column : columns)
         sample_block.insert({column.type, column.name});
     index_granularity_info.initialize(storage, getType(), columns.size());
diff --git a/dbms/src/Storages/MergeTree/MergeTreeMarksLoader.cpp b/dbms/src/Storages/MergeTree/MergeTreeMarksLoader.cpp
index a444f94ba6b..087cada6762 100644
--- a/dbms/src/Storages/MergeTree/MergeTreeMarksLoader.cpp
+++ b/dbms/src/Storages/MergeTree/MergeTreeMarksLoader.cpp
@@ -21,7 +21,7 @@ const MarkInCompressedFile & MergeTreeMarksLoader::getMark(size_t row_index, siz
         loadMarks();
     if (column_index >= columns_num)
         throw Exception("Column index: " + toString(column_index) 
-            + " is out of range (" + toString(columns_num) + ")", ErrorCodes::LOGICAL_ERROR);
+            + " is out of range [0, " + toString(columns_num) + ")", ErrorCodes::LOGICAL_ERROR);
     
     return (*marks)[row_index * columns_num + column_index];
 }
diff --git a/dbms/src/Storages/MutationCommands.h b/dbms/src/Storages/MutationCommands.h
index 5b2a7d906fb..b465740bfde 100644
--- a/dbms/src/Storages/MutationCommands.h
+++ b/dbms/src/Storages/MutationCommands.h
@@ -48,6 +48,7 @@ public:
     void writeText(WriteBuffer & out) const;
     void readText(ReadBuffer & in);
 
+    /// Columns that we need to read except ones needed for expressions.
     Names additional_columns;
 };