diff --git a/dbms/src/IO/WriteBufferFromS3.h b/dbms/src/IO/WriteBufferFromS3.h
index 0eb689e468f..9afda1d14e2 100644
--- a/dbms/src/IO/WriteBufferFromS3.h
+++ b/dbms/src/IO/WriteBufferFromS3.h
@@ -1,25 +1,16 @@
 #pragma once
 
-#include <functional>
 #include <memory>
 #include <vector>
 #include <Core/Types.h>
 #include <IO/ConnectionTimeouts.h>
 #include <IO/HTTPCommon.h>
 #include <IO/BufferWithOwnMemory.h>
-#include <IO/ReadBuffer.h>
-#include <IO/ReadBufferFromIStream.h>
 #include <IO/WriteBuffer.h>
 #include <IO/WriteBufferFromString.h>
 #include <Poco/Net/HTTPBasicCredentials.h>
-#include <Poco/Net/HTTPClientSession.h>
 #include <Poco/Net/HTTPRequest.h>
-#include <Poco/Net/HTTPResponse.h>
 #include <Poco/URI.h>
-#include <Poco/Version.h>
-#include <Common/DNSResolver.h>
-#include <Common/config.h>
-#include <common/logger_useful.h>
 
 
 namespace DB
@@ -36,6 +27,9 @@ private:
     String buffer_string;
     std::unique_ptr<WriteBufferFromString> temporary_buffer;
     size_t last_part_size;
+
+    /// Upload in S3 is made in parts.
+    /// We initiate upload, then upload each part and get ETag as a response, and then finish upload with listing all our parts.
     String upload_id;
     std::vector<String> part_tags;