Added test tool

src/Common/MemoryStatisticsOS.h

@@ -11,6 +11,8 @@ namespace DB
   *
   * Note: a class is used instead of a single function to avoid excessive file open/close on every use.
   * pread is used to avoid lseek.
+  *
+  * Actual performance is from 1 to 5 million iterations per second.
   */
 class MemoryStatisticsOS
 {

src/Common/tests/CMakeLists.txt

@@ -68,3 +68,6 @@ target_link_libraries (symbol_index PRIVATE clickhouse_common_io)
 
 add_executable (chaos_sanitizer chaos_sanitizer.cpp)
 target_link_libraries (chaos_sanitizer PRIVATE clickhouse_common_io)
+
+add_executable (memory_statistics_os_perf memory_statistics_os_perf.cpp)
+target_link_libraries (memory_statistics_os_perf PRIVATE clickhouse_common_io)

src/Common/tests/memory_statistics_os_perf.cpp

@@ -0,0 +1,23 @@
+#include <Common/MemoryStatisticsOS.h>
+#include <iostream>
+
+
+int main(int argc, char ** argv)
+{
+    using namespace DB;
+
+    size_t num_iterations = argc >= 2 ? std::stoull(argv[1]) : 1000000;
+    MemoryStatisticsOS stats;
+
+    uint64_t counter = 0;
+    for (size_t i = 0; i < num_iterations; ++i)
+    {
+        MemoryStatisticsOS::Data data = stats.get();
+        counter += data.resident;
+    }
+
+    std::cerr << (counter / num_iterations) << '\n';
+    return 0;
+}
+
+