Merge pull request #22109 from azat/nested-epoll-wait

Disable async_socket_for_remote/use_hedged_requests for buggy linux kernels

src/Core/SettingsQuirks.cpp

+#include <Core/SettingsQuirks.h>
+#include <Core/Settings.h>
+#include <common/logger_useful.h>
+
+#ifdef __linux__
+#include <linux/version.h>
+#endif
+
+#ifdef __linux__
+/// Detect does epoll_wait with nested epoll fds works correctly.
+/// Polling nested epoll fds from epoll_wait is required for async_socket_for_remote and use_hedged_requests.
+///
+/// It may not be reliable in 5.5+ [1], that has been fixed in 5.7+ [2] or 5.6.13+.
+///
+///   [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=339ddb53d373
+///   [2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0c54a6a44bf3
+bool nestedEpollWorks(Poco::Logger * log)
+{
+    bool nested_epoll_works =
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(5, 5, 0)) && (LINUX_VERSION_CODE < KERNEL_VERSION(5, 6, 13))
+        /// the check is correct since there will be no more 5.5.x releases.
+        false
+#else
+        true
+#endif
+    ;
+
+    if (!nested_epoll_works)
+    {
+        if (log)
+            LOG_WARNING(log, "Nested epoll_wait has some issues on kernels [5.5.0, 5.6.13). You should upgrade it to avoid possible issues.");
+    }
+    return nested_epoll_works;
+}
+#else
+bool nestedEpollWorks(Poco::Logger *) { return true; }
+#endif
+
+namespace DB
+{
+
+/// Update some settings defaults to avoid some known issues.
+void applySettingsQuirks(Settings & settings, Poco::Logger * log)
+{
+    if (!nestedEpollWorks(log))
+    {
+        if (!settings.async_socket_for_remote.changed && settings.async_socket_for_remote)
+        {
+            settings.async_socket_for_remote = false;
+            if (log)
+                LOG_WARNING(log, "async_socket_for_remote has been disabled (you can explicitly enable it still)");
+        }
+        if (!settings.use_hedged_requests.changed && settings.use_hedged_requests)
+        {
+            settings.use_hedged_requests = false;
+            if (log)
+                LOG_WARNING(log, "use_hedged_requests has been disabled (you can explicitly enable it still)");
+        }
+    }
+}
+
+}

src/Core/SettingsQuirks.h

+#pragma once
+
+namespace Poco
+{
+class Logger;
+}
+
+namespace DB
+{
+
+struct Settings;
+
+/// Update some settings defaults to avoid some known issues.
+void applySettingsQuirks(Settings & settings, Poco::Logger * log = nullptr);
+
+}

src/Core/ya.make

@@ -36,6 +36,7 @@ SRCS(
     Settings.cpp
     SettingsEnums.cpp
     SettingsFields.cpp
+    SettingsQuirks.cpp
     SortDescription.cpp
     iostream_debug_helpers.cpp
 

src/Interpreters/Context.cpp

@@ -30,6 +30,7 @@
 #include <TableFunctions/TableFunctionFactory.h>
 #include <Interpreters/ActionLocksManager.h>
 #include <Core/Settings.h>
+#include <Core/SettingsQuirks.h>
 #include <Access/AccessControlManager.h>
 #include <Access/ContextAccess.h>
 #include <Access/EnabledRolesInfo.h>
@@ -1102,6 +1103,7 @@ void Context::applySettingsChanges(const SettingsChanges & changes)
     auto lock = getLock();
     for (const SettingChange & change : changes)
         applySettingChange(change);
+    applySettingsQuirks(settings);
 }
 
 
@@ -2300,6 +2302,8 @@ void Context::setDefaultProfiles(const Poco::Util::AbstractConfiguration & confi
     shared->system_profile_name = config.getString("system_profile", shared->default_profile_name);
     setProfile(shared->system_profile_name);
 
+    applySettingsQuirks(settings, &Poco::Logger::get("SettingsQuirks"));
+
     shared->buffer_profile_name = config.getString("buffer_profile", shared->system_profile_name);
     buffer_context = std::make_shared<Context>(*this);
     buffer_context->setProfile(shared->buffer_profile_name);