diff --git a/bak/concurrency_test.cc b/bak/concurrency_test.cc
new file mode 100644
index 0000000..4cb6a51
--- /dev/null
+++ b/bak/concurrency_test.cc
@@ -0,0 +1,50 @@
+#include <iostream>
+#include <string>
+#include <thread>
+#include <vector>
+
+#include "webcc/client_session.h"
+#include "webcc/logger.h"
+
+// CS Server:
+//   $ concurrency_test 10 http://localhost:55555/patient/query?global_search=ivory&count=200&offset=0&sort_item=birth_date&sort_order=asc
+// GitHub:
+//   $ concurrency_test 10 https://api.github.com/public/events
+
+int main(int argc, const char* argv[]) {
+  if (argc < 3) {
+    std::cerr << "Usage: concurrency_test <workers> <url>" << std::endl;
+    return 1;
+  }
+
+  WEBCC_LOG_INIT("", webcc::LOG_CONSOLE_FILE_OVERWRITE);
+
+  int workers = std::atoi(argv[1]);
+  std::string url = argv[2];
+
+  LOG_USER("Workers: %d", workers);
+  LOG_USER("URL: %s", url.c_str());
+
+  std::vector<std::thread> threads;
+
+  for (int i = 0; i < workers; ++i) {
+    threads.emplace_back([&url]() {
+      webcc::ClientSession session;
+      session.set_timeout(180);
+
+      try {
+        LOG_USER("Start");
+        session.Get(url);
+        LOG_USER("End");
+      } catch (const webcc::Error& error) {
+        LOG_ERRO("Error: %s", error.message().c_str());
+      }
+    });
+  }
+
+  for (int i = 0; i < workers; ++i) {
+    threads[i].join();
+  }
+
+  return 0;
+}
diff --git a/bak/concurrency_test.txt b/bak/concurrency_test.txt
new file mode 100644
index 0000000..1e4f41d
--- /dev/null
+++ b/bak/concurrency_test.txt
@@ -0,0 +1,58 @@
+The client creates 10 threads to send the query request at the same time.
+
+List GitHub public events:
+
+    GET https://api.github.com/events
+
+1 thread
+
+Round 1:
+
+2019-07-05 09:42:23.048, USER,    main,  concurrency_test.cc,   31, URL: http://10.196.98.32:55555
+2019-07-05 09:42:23.063, USER,    main,  concurrency_test.cc,   32, Workers: 1
+2019-07-05 09:42:23.063, USER,   15396,  concurrency_test.cc,   55, Start
+2019-07-05 09:42:25.893, USER,   15396,  concurrency_test.cc,   60, End
+
+Round 2:
+
+2019-07-05 09:42:52.136, USER,    main,  concurrency_test.cc,   31, URL: http://10.196.98.32:55555
+2019-07-05 09:42:52.136, USER,    main,  concurrency_test.cc,   32, Workers: 1
+2019-07-05 09:42:52.136, USER,    5376,  concurrency_test.cc,   55, Start
+2019-07-05 09:42:54.441, USER,    5376,  concurrency_test.cc,   60, End
+
+Round 3:
+
+2019-07-05 09:43:10.768, USER,    main,  concurrency_test.cc,   31, URL: http://10.196.98.32:55555
+2019-07-05 09:43:10.783, USER,    main,  concurrency_test.cc,   32, Workers: 1
+2019-07-05 09:43:10.783, USER,   14620,  concurrency_test.cc,   55, Start
+2019-07-05 09:43:13.405, USER,   14620,  concurrency_test.cc,   60, End
+
+=> 2.5s
+
+
+10 threads:
+
+2019-07-05 09:44:04.016, USER,    main,  concurrency_test.cc,   31, URL: http://10.196.98.32:55555
+2019-07-05 09:44:04.032, USER,    main,  concurrency_test.cc,   32, Workers: 10
+2019-07-05 09:44:04.032, USER,   17348,  concurrency_test.cc,   55, Start
+2019-07-05 09:44:04.032, USER,   10600,  concurrency_test.cc,   55, Start
+2019-07-05 09:44:04.032, USER,    4852,  concurrency_test.cc,   55, Start
+2019-07-05 09:44:04.032, USER,    9480,  concurrency_test.cc,   55, Start
+2019-07-05 09:44:04.032, USER,   10952,  concurrency_test.cc,   55, Start
+2019-07-05 09:44:04.032, USER,    6452,  concurrency_test.cc,   55, Start
+2019-07-05 09:44:04.032, USER,   13060,  concurrency_test.cc,   55, Start
+2019-07-05 09:44:04.032, USER,   14840,  concurrency_test.cc,   55, Start
+2019-07-05 09:44:04.032, USER,    4464,  concurrency_test.cc,   55, Start
+2019-07-05 09:44:04.032, USER,   11304,  concurrency_test.cc,   55, Start
+2019-07-05 09:44:06.739, USER,   10952,  concurrency_test.cc,   60, End
+2019-07-05 09:44:06.823, USER,    9480,  concurrency_test.cc,   60, End
+2019-07-05 09:44:06.839, USER,    4464,  concurrency_test.cc,   60, End
+2019-07-05 09:44:06.861, USER,   14840,  concurrency_test.cc,   60, End
+2019-07-05 09:44:06.908, USER,   11304,  concurrency_test.cc,   60, End
+2019-07-05 09:44:06.908, USER,   13060,  concurrency_test.cc,   60, End
+2019-07-05 09:44:06.908, USER,    4852,  concurrency_test.cc,   60, End
+2019-07-05 09:44:06.923, USER,   10600,  concurrency_test.cc,   60, End
+2019-07-05 09:44:06.977, USER,   17348,  concurrency_test.cc,   60, End
+2019-07-05 09:44:07.193, USER,    6452,  concurrency_test.cc,   60, End
+
+=> 2.5s (still)