diff --git a/dbms/src/Storages/MergeTree/MergeTreeReaderWide.cpp b/dbms/src/Storages/MergeTree/MergeTreeReaderWide.cpp
index b600b9e3bd2..348d6908847 100644
--- a/dbms/src/Storages/MergeTree/MergeTreeReaderWide.cpp
+++ b/dbms/src/Storages/MergeTree/MergeTreeReaderWide.cpp
@@ -50,6 +50,10 @@ MergeTreeReaderWide::MergeTreeReaderWide(const MergeTreeData::DataPartPtr & data
 
 size_t MergeTreeReaderWide::readRows(size_t from_mark, bool continue_reading, size_t max_rows_to_read, Block & res)
 {
+    std::cerr << "(MergeTreeReaderWide::readRows) columns: " << columns.toString() << "\n";
+    std::cerr << "(MergeTreeReaderWide::readRows) from_rows: " << from_mark << "\n";
+    std::cerr << "(MergeTreeReaderWide::readRows) block: " << res.dumpStructure() << "\n";
+
     size_t read_rows = 0;
     try
     {
@@ -178,7 +182,8 @@ void MergeTreeReaderWide::readData(
     size_t from_mark, bool continue_reading, size_t max_rows_to_read,
     bool with_offsets)
 {
-    // std::cerr << "(MergeTreeReaderWide::readData) max_rows_to_read: " << max_rows_to_read << "\n";
+    std::cerr << "(MergeTreeReaderWide::readData) name: " << name << "\n";
+    std::cerr << "(MergeTreeReaderWide::readData) max_rows_to_read: " << max_rows_to_read << "\n";
     auto get_stream_getter = [&](bool stream_for_prefix) -> IDataType::InputStreamGetter
     {
         return [&, stream_for_prefix](const IDataType::SubstreamPath & substream_path) -> ReadBuffer *
diff --git a/dbms/src/Storages/MergeTree/MergeTreeSequentialBlockInputStream.cpp b/dbms/src/Storages/MergeTree/MergeTreeSequentialBlockInputStream.cpp
index 6051b1c36d0..1db67ee2e47 100644
--- a/dbms/src/Storages/MergeTree/MergeTreeSequentialBlockInputStream.cpp
+++ b/dbms/src/Storages/MergeTree/MergeTreeSequentialBlockInputStream.cpp
@@ -51,6 +51,10 @@ MergeTreeSequentialBlockInputStream::MergeTreeSequentialBlockInputStream(
         columns_for_reader = data_part->columns.addTypes(columns_to_read);
     }
 
+    std::cerr << "(MergeTreeSequentialBlockInputStream) table: " << storage.getTableName() << "\n";
+    std::cerr << "(MergeTreeSequentialBlockInputStream) part: " << data_part_->getFullPath() << "\n";
+    std::cerr << "(MergeTreeSequentialBlockInputStream) columns_for_reader: " << columns_for_reader.toString() << "\n";
+
     ReaderSettings reader_settings =
     {
         /// This is hack
@@ -119,6 +123,8 @@ try
         finish();
     }
 
+    std::cerr << "(MergeTreeSequentialBlockInputStream::readImpl) block: " << res.dumpStructure() << "\n";
+
     return res;
 }
 catch (...)