From 6df54611a9da2fde3f76bb04798248d89a7af0b9 Mon Sep 17 00:00:00 2001
From: Azat Khuzhin <a3at.mail@gmail.com>
Date: Sun, 17 Apr 2022 15:01:56 +0300
Subject: [PATCH] Log which taskstats provider is in use

Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
v2: add missing __builtin_unreachable() for gcc built [1]
    [1]: https://s3.amazonaws.com/clickhouse-builds/36351/99e72a960325cc1fb3cd3d6a1b56cf2b1cc2d733/binary_gcc/build_log.log
(cherry picked from commit 2be022cb56b4d8f65f02393c4c6069f409ace4e8)
---
 programs/server/Server.cpp         |  7 ++++++-
 src/Common/ThreadProfileEvents.cpp | 14 ++++++++++++++
 src/Common/ThreadProfileEvents.h   | 18 ++++++++++--------
 3 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/programs/server/Server.cpp b/programs/server/Server.cpp
index 786fff9b0e4..085018fbb87 100644
--- a/programs/server/Server.cpp
+++ b/programs/server/Server.cpp
@@ -1507,7 +1507,8 @@ int Server::main(const std::vector<std::string> & /*args*/)
     }
 
 #if defined(OS_LINUX)
-    if (!TasksStatsCounters::checkIfAvailable())
+    auto tasks_stats_provider = TasksStatsCounters::findBestAvailableProvider();
+    if (tasks_stats_provider == TasksStatsCounters::MetricsProvider::None)
     {
         LOG_INFO(log, "It looks like this system does not have procfs mounted at /proc location,"
             " neither clickhouse-server process has CAP_NET_ADMIN capability."
@@ -1518,6 +1519,10 @@ int Server::main(const std::vector<std::string> & /*args*/)
             " It also doesn't work if you run clickhouse-server inside network namespace as it happens in some containers.",
             executable_path);
     }
+    else
+    {
+        LOG_INFO(log, "Tasks stats provider: {}", TasksStatsCounters::metricsProviderString(tasks_stats_provider));
+    }
 
     if (!hasLinuxCapability(CAP_SYS_NICE))
     {
diff --git a/src/Common/ThreadProfileEvents.cpp b/src/Common/ThreadProfileEvents.cpp
index e28e5d3e85e..1a7b4d88322 100644
--- a/src/Common/ThreadProfileEvents.cpp
+++ b/src/Common/ThreadProfileEvents.cpp
@@ -67,6 +67,20 @@ namespace ProfileEvents
 namespace DB
 {
 
+const char * TasksStatsCounters::metricsProviderString(MetricsProvider provider)
+{
+    switch (provider)
+    {
+        case MetricsProvider::None:
+            return "none";
+        case MetricsProvider::Procfs:
+            return "procfs";
+        case MetricsProvider::Netlink:
+            return "netlink";
+    }
+    __builtin_unreachable();
+}
+
 bool TasksStatsCounters::checkIfAvailable()
 {
     return findBestAvailableProvider() != MetricsProvider::None;
diff --git a/src/Common/ThreadProfileEvents.h b/src/Common/ThreadProfileEvents.h
index befd759c71b..0f2ad7dfd74 100644
--- a/src/Common/ThreadProfileEvents.h
+++ b/src/Common/ThreadProfileEvents.h
@@ -176,7 +176,17 @@ extern PerfEventsCounters current_thread_counters;
 class TasksStatsCounters
 {
 public:
+    enum class MetricsProvider
+    {
+        None,
+        Procfs,
+        Netlink,
+    };
+
+    static const char * metricsProviderString(MetricsProvider provider);
     static bool checkIfAvailable();
+    static MetricsProvider findBestAvailableProvider();
+
     static std::unique_ptr<TasksStatsCounters> create(UInt64 tid);
 
     void reset();
@@ -186,16 +196,8 @@ private:
     ::taskstats stats;  //-V730_NOINIT
     std::function<::taskstats()> stats_getter;
 
-    enum class MetricsProvider
-    {
-        None,
-        Procfs,
-        Netlink
-    };
-
     explicit TasksStatsCounters(UInt64 tid, MetricsProvider provider);
 
-    static MetricsProvider findBestAvailableProvider();
     static void incrementProfileEvents(const ::taskstats & prev, const ::taskstats & curr, ProfileEvents::Counters & profile_events);
 };