From 1aa89ed63a35a7e7b898eefd3cc7bacbd40a89c3 Mon Sep 17 00:00:00 2001
From: Alexey Milovidov <milovidov@yandex-team.ru>
Date: Wed, 14 Nov 2018 04:20:46 +0300
Subject: [PATCH] Fixed code after review #3553

---
 dbms/programs/server/Server.cpp | 31 +++++++++++--------------------
 dbms/programs/server/config.xml |  6 ++++++
 2 files changed, 17 insertions(+), 20 deletions(-)

diff --git a/dbms/programs/server/Server.cpp b/dbms/programs/server/Server.cpp
index c40962d5ebe..0937cf4b84a 100644
--- a/dbms/programs/server/Server.cpp
+++ b/dbms/programs/server/Server.cpp
@@ -131,39 +131,30 @@ int Server::main(const std::vector<std::string> & /*args*/)
     }
 
     const auto memory_amount = getMemoryAmount();
-    { /// After full config loaded
+
 #if defined(__linux__)
-        if (config().getBool("mlock_executable",
-            false // TODO: uncomment after tests:
-/*
-#if NDEBUG
-            memory_amount > 16000000000
-                ? true // Change me to true in future
-                : false // Dont mlock if we have less than 16G ram
-#else
-            false
-#endif
-*/
-        ))
+    /// After full config loaded
+    {
+        if (config().getBool("mlock_executable", false))
         {
             if (hasLinuxCapability(CAP_IPC_LOCK))
             {
+                LOG_TRACE(log, "Will mlockall to prevent executable memory from being paged out. It may take a few seconds.");
                 if (0 != mlockall(MCL_CURRENT))
                     LOG_WARNING(log, "Failed mlockall: " + errnoToString());
                 else
-                    LOG_TRACE(log, "Binary mlock'ed");
+                    LOG_TRACE(log, "The memory map of clickhouse executable has been mlock'ed");
             }
             else
             {
-                 LOG_INFO(log, "It looks like the process has no CAP_IPC_LOCK capability, binary mlock will be disabled."
-                      " It could happen due to incorrect ClickHouse package installation."
-                      " You could resolve the problem manually with 'sudo setcap cap_ipc_lock=+ep /usr/bin/clickhouse'."
-                      " Note that it will not work on 'nosuid' mounted filesystems.");
-
+                LOG_INFO(log, "It looks like the process has no CAP_IPC_LOCK capability, binary mlock will be disabled."
+                    " It could happen due to incorrect ClickHouse package installation."
+                    " You could resolve the problem manually with 'sudo setcap cap_ipc_lock=+ep /usr/bin/clickhouse'."
+                    " Note that it will not work on 'nosuid' mounted filesystems.");
             }
         }
-#endif
     }
+#endif
 
     std::string path = getCanonicalPath(config().getString("path"));
     std::string default_database = config().getString("default_database", "default");
diff --git a/dbms/programs/server/config.xml b/dbms/programs/server/config.xml
index e461d49d522..051f6f7fb2b 100644
--- a/dbms/programs/server/config.xml
+++ b/dbms/programs/server/config.xml
@@ -145,6 +145,12 @@
     -->
     <!-- <umask>022</umask> -->
 
+    <!-- Perform mlockall after startup to lower first queries latency
+          and to prevent clickhouse executable from being paged out under high IO load.
+         Enabling this option is recommended but will lead to increased startup time for up to a few seconds.
+    -->
+    <mlock_executable>false</mlock_executable>
+
     <!-- Configuration of clusters that could be used in Distributed tables.
          https://clickhouse.yandex/docs/en/table_engines/distributed/
       -->