text: #include "Server.h"
  
  #include <memory>
  #include <sys/resource.h>
  #include <sys/stat.h>
  #include <sys/types.h>
  #include <errno.h>
  #include <pwd.h>
  #include <unistd.h>
  #include <Poco/Version.h>
  #include <Poco/DirectoryIterator.h>
  #include <Poco/Net/HTTPServer.h>
  #include <Poco/Net/NetException.h>
  #include <Poco/Util/HelpFormatter.h>
  #include <ext/scope_guard.h>
  #include <common/logger_useful.h>
  #include <common/phdr_cache.h>
  #include <common/ErrorHandlers.h>
  #include <common/getMemoryAmount.h>
  #include <common/coverage.h>
  #include <Common/ClickHouseRevision.h>
  #include <Common/DNSResolver.h>
  #include <Common/CurrentMetrics.h>
  #include <Common/Macros.h>
  #include <Common/StringUtils/StringUtils.h>
  #include <Common/ZooKeeper/ZooKeeper.h>
  #include <Common/ZooKeeper/ZooKeeperNodeCache.h>
  #include <common/getFQDNOrHostName.h>
  #include <Common/getMultipleKeysFromConfig.h>
  #include <Common/getNumberOfPhysicalCPUCores.h>
  #include <Common/getExecutablePath.h>
  #include <Common/ThreadProfileEvents.h>
  #include <Common/ThreadStatus.h>
  #include <IO/HTTPCommon.h>
  #include <IO/UseSSL.h>
  #include <Interpreters/AsynchronousMetrics.h>
  #include <Interpreters/DDLWorker.h>
  #include <Interpreters/ExternalDictionariesLoader.h>
  #include <Interpreters/ExternalModelsLoader.h>
  #include <Interpreters/ProcessList.h>
  #include <Interpreters/loadMetadata.h>
  #include <Interpreters/DatabaseCatalog.h>
  #include <Interpreters/DNSCacheUpdater.h>
  #include <Interpreters/SystemLog.cpp>
  #include <Interpreters/ExternalLoaderXMLConfigRepository.h>
  #include <Access/AccessControlManager.h>
  #include <Storages/StorageReplicatedMergeTree.h>
  #include <Storages/System/attachSystemTables.h>
  #include <AggregateFunctions/registerAggregateFunctions.h>
  #include <Functions/registerFunctions.h>
  #include <TableFunctions/registerTableFunctions.h>
  #include <Storages/registerStorages.h>
  #include <Dictionaries/registerDictionaries.h>
  #include <Disks/registerDisks.h>
  #include <Common/Config/ConfigReloader.h>
  #include "HTTPHandlerFactory.h"
  #include "MetricsTransmitter.h"
  #include <Common/StatusFile.h>
  #include "TCPHandlerFactory.h"
  #include <Common/SensitiveDataMasker.h>
  #include <Common/ThreadFuzzer.h>
  #include "MySQLHandlerFactory.h"
  
  #if !defined(ARCADIA_BUILD)
  #    include "config_core.h"
  #    include "Common/config_version.h"
  #endif
  
  #if defined(OS_LINUX)
  #    include <sys/mman.h>
  #    include <Common/hasLinuxCapability.h>
  #endif
  
  #if USE_SSL
  #    include <Poco/Net/Context.h>
  #    include <Poco/Net/SecureServerSocket.h>
  #endif
  
  namespace CurrentMetrics
  {
      extern const Metric Revision;
      extern const Metric VersionInteger;
      extern const Metric MemoryTracking;
  }
  
  namespace
  {
  
  void setupTmpPath(Logger * log, const std::string & path)
  {
      LOG_DEBUG(log, "Setting up " << path << " to store temporary data in it");
  
      Poco::File(path).createDirectories();
  
      /// Clearing old temporary files.
      Poco::DirectoryIterator dir_end;
      for (Poco::DirectoryIterator it(path); it != dir_end; ++it)
      {
          if (it->isFile() && startsWith(it.name(), "tmp"))
          {
              LOG_DEBUG(log, "Removing old temporary file " << it->path());
              it->remove();
          }
          else
              LOG_DEBUG(log, "Skipped file in temporary path " << it->path());
      }
  }
  
  }
  
  namespace DB
  {
  
  namespace ErrorCodes
  {
      extern const int NO_ELEMENTS_IN_CONFIG;
      extern const int SUPPORT_IS_DISABLED;
      extern const int ARGUMENT_OUT_OF_BOUND;
      extern const int EXCESSIVE_ELEMENT_IN_CONFIG;
      extern const int INVALID_CONFIG_PARAMETER;
      extern const int SYSTEM_ERROR;
      extern const int FAILED_TO_GETPWUID;
      extern const int MISMATCHING_USERS_FOR_PROCESS_AND_DATA;
      extern const int NETWORK_ERROR;
  }
  
  
  static std::string getCanonicalPath(std::string && path)
  {
      Poco::trimInPlace(path);
      if (path.empty())
          throw Exception("path configuration parameter is empty", ErrorCodes::INVALID_CONFIG_PARAMETER);
      if (path.back() != '/')
          path += '/';
      return std::move(path);
  }
  
  static std::string getUserName(uid_t user_id)
  {
      /// Try to convert user id into user name.
      auto buffer_size = sysconf(_SC_GETPW_R_SIZE_MAX);
      if (buffer_size <= 0)
          buffer_size = 1024;
      std::string buffer;
      buffer.reserve(buffer_size);
  
      struct passwd passwd_entry;
      struct passwd * result = nullptr;
      const auto error = getpwuid_r(user_id, &passwd_entry, buffer.data(), buffer_size, &result);
  
      if (error)
          throwFromErrno("Failed to find user name for " + toString(user_id), ErrorCodes::FAILED_TO_GETPWUID, error);
      else if (result)
          return result->pw_name;
      return toString(user_id);
  }
  
  void Server::uninitialize()
  {
      logger().information("shutting down");
      BaseDaemon::uninitialize();
  }
  
  int Server::run()
  {
      if (config().hasOption("help"))
      {
          Poco::Util::HelpFormatter help_formatter(Server::options());
          std::stringstream header;
          header << commandName() << " [OPTION] [-- [ARG]...]\n";
          header << "positional arguments can be used to rewrite config.xml properties, for example, --http_port=8010";
          help_formatter.setHeader(header.str());
          help_formatter.format(std::cout);
          return 0;
      }
      if (config().hasOption("version"))
      {
          std::cout << DBMS_NAME << " server version " << VERSION_STRING << VERSION_OFFICIAL << "." << std::endl;
          return 0;
      }
      return Application::run(); // NOLINT
  }
  
  void Server::initialize(Poco::Util::Application & self)
  {
      BaseDaemon::initialize(self);
      logger().information("starting up");
  }
  
  std::string Server::getDefaultCorePath() const
  {
      return getCanonicalPath(config().getString("path", DBMS_DEFAULT_PATH)) + "cores";
  }
  
  void Server::defineOptions(Poco::Util::OptionSet & options)
  {
      options.addOption(
          Poco::Util::Option("help", "h", "show help and exit")
              .required(false)
              .repeatable(false)
              .binding("help"));
      options.addOption(
          Poco::Util::Option("version", "V", "show version and exit")
              .required(false)
              .repeatable(false)
              .binding("version"));
      BaseDaemon::defineOptions(options);
  }
  
  int Server::main(const std::vector<std::string> & /*args*/)
  {
      Logger * log = &logger();
      UseSSL use_ssl;
  
      ThreadStatus thread_status;
  
      registerFunctions();
      registerAggregateFunctions();
      registerTableFunctions();
      registerStorages();
      registerDictionaries();
      registerDisks();
  
      CurrentMetrics::set(CurrentMetrics::Revision, ClickHouseRevision::get());
      CurrentMetrics::set(CurrentMetrics::VersionInteger, ClickHouseRevision::getVersionInteger());
  
      if (ThreadFuzzer::instance().isEffective())
          LOG_WARNING(log, "ThreadFuzzer is enabled. Application will run slowly and unstable.");
  
      /** Context contains all that query execution is dependent:
        *  settings, available functions, data types, aggregate functions, databases...
        */
      auto shared_context = Context::createShared();
      auto global_context = std::make_unique<Context>(Context::createGlobal(shared_context.get()));
      global_context_ptr = global_context.get();
  
      global_context->makeGlobalContext();
      global_context->setApplicationType(Context::ApplicationType::SERVER);
  
      bool has_zookeeper = config().has("zookeeper");
  
      zkutil::ZooKeeperNodeCache main_config_zk_node_cache([&] { return global_context->getZooKeeper(); });
      zkutil::EventPtr main_config_zk_changed_event = std::make_shared<Poco::Event>();
      if (loaded_config.has_zk_includes)
      {
          auto old_configuration = loaded_config.configuration;
          ConfigProcessor config_processor(config_path);
          loaded_config = config_processor.loadConfigWithZooKeeperIncludes(
              main_config_zk_node_cache, main_config_zk_changed_event, /* fallback_to_preprocessed = */ true);
          config_processor.savePreprocessedConfig(loaded_config, config().getString("path", DBMS_DEFAULT_PATH));
          config().removeConfiguration(old_configuration.get());
          config().add(loaded_config.configuration.duplicate(), PRIO_DEFAULT, false);
      }
  
      const auto memory_amount = getMemoryAmount();
  
  #if defined(OS_LINUX)
      std::string executable_path = getExecutablePath();
      if (executable_path.empty())
          executable_path = "/usr/bin/clickhouse";    /// It is used for information messages.
  
      /// 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(ErrorCodes::SYSTEM_ERROR));
                  else
                      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 " << executable_path << "'."
                      " Note that it will not work on 'nosuid' mounted filesystems.");
              }
          }
      }
  #endif
  
      global_context->setRemoteHostFilter(config());
  
      std::string path = getCanonicalPath(config().getString("path", DBMS_DEFAULT_PATH));
      std::string default_database = config().getString("default_database", "default");
  
      /// Check that the process' user id matches the owner of the data.
      const auto effective_user_id = geteuid();
      struct stat statbuf;
      if (stat(path.c_str(), &statbuf) == 0 && effective_user_id != statbuf.st_uid)
      {
          const auto effective_user = getUserName(effective_user_id);
          const auto data_owner = getUserName(statbuf.st_uid);
          std::string message = "Effective user of the process (" + effective_user +
              ") does not match the owner of the data (" + data_owner + ").";
          if (effective_user_id == 0)
          {
              message += " Run under 'sudo -u " + data_owner + "'.";
              throw Exception(message, ErrorCodes::MISMATCHING_USERS_FOR_PROCESS_AND_DATA);
          }
          else
          {
              LOG_WARNING(log, message);
          }
      }
  
      global_context->setPath(path);
  
      StatusFile status{path + "status"};
  
      SCOPE_EXIT({
          /** Ask to cancel background jobs all table engines,
            *  and also query_log.
            * It is important to do early, not in destructor of Context, because
            *  table engines could use Context on destroy.
            */
          LOG_INFO(log, "Shutting down storages.");
  
          global_context->shutdown();
  
          LOG_DEBUG(log, "Shut down storages.");
  
          /** Explicitly destroy Context. It is more convenient than in destructor of Server, because logger is still available.
            * At this moment, no one could own shared part of Context.
            */
          global_context_ptr = nullptr;
          global_context.reset();
          shared_context.reset();
          LOG_DEBUG(log, "Destroyed global context.");
      });
  
      /// Try to increase limit on number of open files.
      {
          rlimit rlim;
          if (getrlimit(RLIMIT_NOFILE, &rlim))
              throw Poco::Exception("Cannot getrlimit");
  
          if (rlim.rlim_cur == rlim.rlim_max)
          {
              LOG_DEBUG(log, "rlimit on number of file descriptors is " << rlim.rlim_cur);
          }
          else
          {
              rlim_t old = rlim.rlim_cur;
              rlim.rlim_cur = config().getUInt("max_open_files", rlim.rlim_max);
              int rc = setrlimit(RLIMIT_NOFILE, &rlim);
              if (rc != 0)
                  LOG_WARNING(log,
                      "Cannot set max number of file descriptors to " << rlim.rlim_cur
                          << ". Try to specify max_open_files according to your system limits. error: "
                          << strerror(errno));
              else
                  LOG_DEBUG(log, "Set max number of file descriptors to " << rlim.rlim_cur << " (was " << old << ").");
          }
      }
  
      static ServerErrorHandler error_handler;
      Poco::ErrorHandler::set(&error_handler);
  
      /// Initialize DateLUT early, to not interfere with running time of first query.
      LOG_DEBUG(log, "Initializing DateLUT.");
      DateLUT::instance();
      LOG_TRACE(log, "Initialized DateLUT with time zone '" << DateLUT::instance().getTimeZone() << "'.");
  
  
      /// Storage with temporary data for processing of heavy queries.
      {
          std::string tmp_path = config().getString("tmp_path", path + "tmp/");
          std::string tmp_policy = config().getString("tmp_policy", "");
          const VolumePtr & volume = global_context->setTemporaryStorage(tmp_path, tmp_policy);
          for (const DiskPtr & disk : volume->disks)
              setupTmpPath(log, disk->getPath());
      }
  
      /** Directory with 'flags': files indicating temporary settings for the server set by system administrator.
        * Flags may be cleared automatically after being applied by the server.
        * Examples: do repair of local data; clone all replicated tables from replica.
        */
      {
          Poco::File(path + "flags/").createDirectories();
          global_context->setFlagsPath(path + "flags/");
      }
  
      /** Directory with user provided files that are usable by 'file' table function.
        */
      {
  
          std::string user_files_path = config().getString("user_files_path", path + "user_files/");
          global_context->setUserFilesPath(user_files_path);
          Poco::File(user_files_path).createDirectories();
      }
  
      {
          std::string dictionaries_lib_path = config().getString("dictionaries_lib_path", path + "dictionaries_lib/");
          global_context->setDictionariesLibPath(dictionaries_lib_path);
          Poco::File(dictionaries_lib_path).createDirectories();
      }
  
      {
          /// Directory with metadata of tables, which was marked as dropped by Atomic database
          Poco::File(path + "metadata_dropped/").createDirectories();
      }
  
      if (config().has("interserver_http_port") && config().has("interserver_https_port"))
          throw Exception("Both http and https interserver ports are specified", ErrorCodes::EXCESSIVE_ELEMENT_IN_CONFIG);
  
      static const auto interserver_tags =
      {
          std::make_tuple("interserver_http_host", "interserver_http_port", "http"),
          std::make_tuple("interserver_https_host", "interserver_https_port", "https")
      };
  
      for (auto [host_tag, port_tag, scheme] : interserver_tags)
      {
          if (config().has(port_tag))
          {
              String this_host = config().getString(host_tag, "");
  
              if (this_host.empty())
              {
                  this_host = getFQDNOrHostName();
                  LOG_DEBUG(log,
                      "Configuration parameter '" + String(host_tag) + "' doesn't exist or exists and empty. Will use '" + this_host
                          + "' as replica host.");
              }
  
              String port_str = config().getString(port_tag);
              int port = parse<int>(port_str);
  
              if (port < 0 || port > 0xFFFF)
                  throw Exception("Out of range '" + String(port_tag) + "': " + toString(port), ErrorCodes::ARGUMENT_OUT_OF_BOUND);
  
              global_context->setInterserverIOAddress(this_host, port);
              global_context->setInterserverScheme(scheme);
          }
      }
  
      if (config().has("interserver_http_credentials"))
      {
          String user = config().getString("interserver_http_credentials.user", "");
          String password = config().getString("interserver_http_credentials.password", "");
  
          if (user.empty())
              throw Exception("Configuration parameter interserver_http_credentials user can't be empty", ErrorCodes::NO_ELEMENTS_IN_CONFIG);
  
          global_context->setInterserverCredentials(user, password);
      }
  
      if (config().has("macros"))
          global_context->setMacros(std::make_unique<Macros>(config(), "macros"));
  
      /// Initialize main config reloader.
      std::string include_from_path = config().getString("include_from", "/etc/metrika.xml");
  
      if (config().has("query_masking_rules"))
      {
          SensitiveDataMasker::setInstance(std::make_unique<SensitiveDataMasker>(config(), "query_masking_rules"));
      }
  
      auto main_config_reloader = std::make_unique<ConfigReloader>(config_path,
          include_from_path,
          config().getString("path", ""),
          std::move(main_config_zk_node_cache),
          main_config_zk_changed_event,
          [&](ConfigurationPtr config)
          {
              // FIXME logging-related things need synchronization -- see the 'Logger * log' saved
              // in a lot of places. For now, disable updating log configuration without server restart.
              //setTextLog(global_context->getTextLog());
              //buildLoggers(*config, logger());
              global_context->setClustersConfig(config);
              global_context->setMacros(std::make_unique<Macros>(*config, "macros"));
  
              /// Setup protection to avoid accidental DROP for big tables (that are greater than 50 GB by default)
              if (config->has("max_table_size_to_drop"))
                  global_context->setMaxTableSizeToDrop(config->getUInt64("max_table_size_to_drop"));
  
              if (config->has("max_partition_size_to_drop"))
                  global_context->setMaxPartitionSizeToDrop(config->getUInt64("max_partition_size_to_drop"));
  
              global_context->updateStorageConfiguration(*config);
          },
          /* already_loaded = */ true);
  
      /// Initialize users config reloader.
      std::string users_config_path = config().getString("users_config", config_path);
      /// If path to users' config isn't absolute, try guess its root (current) dir.
      /// At first, try to find it in dir of main config, after will use current dir.
      if (users_config_path.empty() || users_config_path[0] != '/')
      {
          std::string config_dir = Poco::Path(config_path).parent().toString();
          if (Poco::File(config_dir + users_config_path).exists())
              users_config_path = config_dir + users_config_path;
      }
      auto users_config_reloader = std::make_unique<ConfigReloader>(users_config_path,
          include_from_path,
          config().getString("path", ""),
          zkutil::ZooKeeperNodeCache([&] { return global_context->getZooKeeper(); }),
          std::make_shared<Poco::Event>(),
          [&](ConfigurationPtr config) { global_context->setUsersConfig(config); },
          /* already_loaded = */ false);
  
      /// Reload config in SYSTEM RELOAD CONFIG query.
      global_context->setConfigReloadCallback([&]()
      {
          main_config_reloader->reload();
          users_config_reloader->reload();
      });
  
      /// Sets a local directory storing information about access control.
      std::string access_control_local_path = config().getString("access_control_path", "");
      if (!access_control_local_path.empty())
          global_context->getAccessControlManager().setLocalDirectory(access_control_local_path);
  
      /// Limit on total number of concurrently executed queries.
      global_context->getProcessList().setMaxSize(config().getInt("max_concurrent_queries", 0));
  
      /// Set up caches.
  
      /// Lower cache size on low-memory systems.
      double cache_size_to_ram_max_ratio = config().getDouble("cache_size_to_ram_max_ratio", 0.5);
      size_t max_cache_size = memory_amount * cache_size_to_ram_max_ratio;
  
      /// Size of cache for uncompressed blocks. Zero means disabled.
      size_t uncompressed_cache_size = config().getUInt64("uncompressed_cache_size", 0);
      if (uncompressed_cache_size > max_cache_size)
      {
          uncompressed_cache_size = max_cache_size;
          LOG_INFO(log, "Uncompressed cache size was lowered to " << formatReadableSizeWithBinarySuffix(uncompressed_cache_size)
              << " because the system has low amount of memory");
      }
      global_context->setUncompressedCache(uncompressed_cache_size);
  
      /// Load global settings from default_profile and system_profile.
      global_context->setDefaultProfiles(config());
      const Settings & settings = global_context->getSettingsRef();
  
      /// Size of cache for marks (index of MergeTree family of tables). It is mandatory.
      size_t mark_cache_size = config().getUInt64("mark_cache_size");
      if (!mark_cache_size)
          LOG_ERROR(log, "Too low mark cache size will lead to severe performance degradation.");
      if (mark_cache_size > max_cache_size)
      {
          mark_cache_size = max_cache_size;
          LOG_INFO(log, "Mark cache size was lowered to " << formatReadableSizeWithBinarySuffix(uncompressed_cache_size)
              << " because the system has low amount of memory");
      }
      global_context->setMarkCache(mark_cache_size);
  
  #if USE_EMBEDDED_COMPILER
      size_t compiled_expression_cache_size = config().getUInt64("compiled_expression_cache_size", 500);
      if (compiled_expression_cache_size)
          global_context->setCompiledExpressionCache(compiled_expression_cache_size);
  #endif
  
      /// Set path for format schema files
      auto format_schema_path = Poco::File(config().getString("format_schema_path", path + "format_schemas/"));
      global_context->setFormatSchemaPath(format_schema_path.path());
      format_schema_path.createDirectories();
  
      /// Limit on total memory usage
      size_t max_server_memory_usage = config().getUInt64("max_server_memory_usage", 0);
  
      double max_server_memory_usage_to_ram_ratio = config().getDouble("max_server_memory_usage_to_ram_ratio", 0.9);
      size_t default_max_server_memory_usage = memory_amount * max_server_memory_usage_to_ram_ratio;
  
      if (max_server_memory_usage == 0)
      {
          max_server_memory_usage = default_max_server_memory_usage;
          LOG_INFO(log, "Setting max_server_memory_usage was set to " << formatReadableSizeWithBinarySuffix(max_server_memory_usage));
      }
      else if (max_server_memory_usage > default_max_server_memory_usage)
      {
          max_server_memory_usage = default_max_server_memory_usage;
          LOG_INFO(log, "Setting max_server_memory_usage was lowered to " << formatReadableSizeWithBinarySuffix(max_server_memory_usage)
              << " because the system has low amount of memory");
      }
  
      total_memory_tracker.setOrRaiseHardLimit(max_server_memory_usage);
      total_memory_tracker.setDescription("(total)");
      total_memory_tracker.setMetric(CurrentMetrics::MemoryTracking);
  
      LOG_INFO(log, "Loading metadata from " + path);
  
      try
      {
          loadMetadataSystem(*global_context);
          /// After attaching system databases we can initialize system log.
          global_context->initializeSystemLogs();
          /// After the system database is created, attach virtual system tables (in addition to query_log and part_log)
          attachSystemTablesServer(*DatabaseCatalog::instance().getSystemDatabase(), has_zookeeper);
          /// Then, load remaining databases
          loadMetadata(*global_context, default_database);
          DatabaseCatalog::instance().loadDatabases();
      }
      catch (...)
      {
          tryLogCurrentException(log, "Caught exception while loading metadata");
          throw;
      }
      LOG_DEBUG(log, "Loaded metadata.");
  
      /// Init trace collector only after trace_log system table was created
      /// Disable it if we collect test coverage information, because it will work extremely slow.
      ///
      /// It also cannot work with sanitizers.
      /// Sanitizers are using quick "frame walking" stack unwinding (this implies -fno-omit-frame-pointer)
      /// And they do unwinding frequently (on every malloc/free, thread/mutex operations, etc).
      /// They change %rbp during unwinding and it confuses libunwind if signal comes during sanitizer unwinding
      ///  and query profiler decide to unwind stack with libunwind at this moment.
      ///
      /// Symptoms: you'll get silent Segmentation Fault - without sanitizer message and without usual ClickHouse diagnostics.
      ///
      /// Look at compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.h
      ///
  #if USE_UNWIND && !WITH_COVERAGE && !defined(SANITIZER)
      /// Profilers cannot work reliably with any other libunwind or without PHDR cache.
      if (hasPHDRCache())
      {
          global_context->initializeTraceCollector();
  
          /// Set up server-wide memory profiler (for total memory tracker).
          UInt64 total_memory_profiler_step = config().getUInt64("total_memory_profiler_step", 0);
          if (total_memory_profiler_step)
          {
              total_memory_tracker.setOrRaiseProfilerLimit(total_memory_profiler_step);
              total_memory_tracker.setProfilerStep(total_memory_profiler_step);
          }
  
          double total_memory_tracker_sample_probability = config().getDouble("total_memory_tracker_sample_probability", 0);
          if (total_memory_tracker_sample_probability)
          {
              total_memory_tracker.setSampleProbability(total_memory_tracker_sample_probability);
          }
      }
  #endif
  
      /// Describe multiple reasons when query profiler cannot work.
  
  #if !USE_UNWIND
      LOG_INFO(log, "Query Profiler and TraceCollector are disabled because they cannot work without bundled unwind (stack unwinding) library.");
  #endif
  
  #if WITH_COVERAGE
      LOG_INFO(log, "Query Profiler and TraceCollector are disabled because they work extremely slow with test coverage.");
  #endif
  
  #if defined(SANITIZER)
      LOG_INFO(log, "Query Profiler and TraceCollector are disabled because they cannot work under sanitizers"
          " when two different stack unwinding methods will interfere with each other.");
  #endif
  
      if (!hasPHDRCache())
          LOG_INFO(log, "Query Profiler and TraceCollector are disabled because they require PHDR cache to be created"
              " (otherwise the function 'dl_iterate_phdr' is not lock free and not async-signal safe).");
  
      global_context->setCurrentDatabase(default_database);
  
      if (has_zookeeper && config().has("distributed_ddl"))
      {
          /// DDL worker should be started after all tables were loaded
          String ddl_zookeeper_path = config().getString("distributed_ddl.path", "/clickhouse/task_queue/ddl/");
          global_context->setDDLWorker(std::make_unique<DDLWorker>(ddl_zookeeper_path, *global_context, &config(), "distributed_ddl"));
      }
  
      std::unique_ptr<DNSCacheUpdater> dns_cache_updater;
      if (config().has("disable_internal_dns_cache") && config().getInt("disable_internal_dns_cache"))
      {
          /// Disable DNS caching at all
          DNSResolver::instance().setDisableCacheFlag();
      }
      else
      {
          /// Initialize a watcher periodically updating DNS cache
          dns_cache_updater = std::make_unique<DNSCacheUpdater>(*global_context, config().getInt("dns_cache_update_period", 15));
      }
  
  #if defined(OS_LINUX)
      if (!TasksStatsCounters::checkIfAvailable())
      {
          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."
              " 'taskstats' performance statistics will be disabled."
              " It could happen due to incorrect ClickHouse package installation."
              " You can try to resolve the problem manually with 'sudo setcap cap_net_admin=+ep " << executable_path << "'."
              " Note that it will not work on 'nosuid' mounted filesystems."
              " It also doesn't work if you run clickhouse-server inside network namespace as it happens in some containers.");
      }
  
      if (!hasLinuxCapability(CAP_SYS_NICE))
      {
          LOG_INFO(log, "It looks like the process has no CAP_SYS_NICE capability, the setting 'os_thread_nice' will have no effect."
              " It could happen due to incorrect ClickHouse package installation."
              " You could resolve the problem manually with 'sudo setcap cap_sys_nice=+ep " << executable_path << "'."
              " Note that it will not work on 'nosuid' mounted filesystems.");
      }
  #else
      LOG_INFO(log, "TaskStats is not implemented for this OS. IO accounting will be disabled.");
  #endif
  
      {
          Poco::Timespan keep_alive_timeout(config().getUInt("keep_alive_timeout", 10), 0);
  
          Poco::ThreadPool server_pool(3, config().getUInt("max_connections", 1024));
          Poco::Net::HTTPServerParams::Ptr http_params = new Poco::Net::HTTPServerParams;
          http_params->setTimeout(settings.http_receive_timeout);
          http_params->setKeepAliveTimeout(keep_alive_timeout);
  
          std::vector<std::unique_ptr<Poco::Net::TCPServer>> servers;
  
          std::vector<std::string> listen_hosts = DB::getMultipleValuesFromConfig(config(), "", "listen_host");
  
          bool listen_try = config().getBool("listen_try", false);
          if (listen_hosts.empty())
          {
              listen_hosts.emplace_back("::1");
              listen_hosts.emplace_back("127.0.0.1");
              listen_try = true;
          }
  
          auto make_socket_address = [&](const std::string & host, UInt16 port)
          {
              Poco::Net::SocketAddress socket_address;
              try
              {
                  socket_address = Poco::Net::SocketAddress(host, port);
              }
              catch (const Poco::Net::DNSException & e)
              {
                  const auto code = e.code();
                  if (code == EAI_FAMILY
  #if defined(EAI_ADDRFAMILY)
                      || code == EAI_ADDRFAMILY
  #endif
                      )
                  {
                      LOG_ERROR(log,
                          "Cannot resolve listen_host (" << host << "), error " << e.code() << ": " << e.message() << ". "
                          "If it is an IPv6 address and your host has disabled IPv6, then consider to "
                          "specify IPv4 address to listen in <listen_host> element of configuration "
                          "file. Example: <listen_host>0.0.0.0</listen_host>");
                  }
  
                  throw;
              }
              return socket_address;
          };
  
          auto socket_bind_listen = [&](auto & socket, const std::string & host, UInt16 port, [[maybe_unused]] bool secure = false)
          {
                 auto address = make_socket_address(host, port);
  #if !defined(POCO_CLICKHOUSE_PATCH) || POCO_VERSION < 0x01090100
                 if (secure)
                     /// Bug in old (<1.9.1) poco, listen() after bind() with reusePort param will fail because have no implementation in SecureServerSocketImpl
                     /// https://github.com/pocoproject/poco/pull/2257
                     socket.bind(address, /* reuseAddress = */ true);
                 else
  #endif
  #if POCO_VERSION < 0x01080000
                     socket.bind(address, /* reuseAddress = */ true);
  #else
                     socket.bind(address, /* reuseAddress = */ true, /* reusePort = */ config().getBool("listen_reuse_port", false));
  #endif
  
                 socket.listen(/* backlog = */ config().getUInt("listen_backlog", 64));
  
                 return address;
          };
  
          /// This object will periodically calculate some metrics.
          AsynchronousMetrics async_metrics(*global_context);
          attachSystemTablesAsync(*DatabaseCatalog::instance().getSystemDatabase(), async_metrics);
  
          for (const auto & listen_host : listen_hosts)
          {
              auto create_server = [&](const char * port_name, auto && func)
              {
                  /// For testing purposes, user may omit tcp_port or http_port or https_port in configuration file.
                  if (!config().has(port_name))
                      return;
  
                  auto port = config().getInt(port_name);
                  try
                  {
                      func(port);
                  }
                  catch (const Poco::Exception &)
                  {
                      std::string message = "Listen [" + listen_host + "]:" + std::to_string(port) + " failed: " + getCurrentExceptionMessage(false);
  
                      if (listen_try)
                      {
                          LOG_ERROR(log, message
                              << ". If it is an IPv6 or IPv4 address and your host has disabled IPv6 or IPv4, then consider to "
                              "specify not disabled IPv4 or IPv6 address to listen in <listen_host> element of configuration "
                              "file. Example for disabled IPv6: <listen_host>0.0.0.0</listen_host> ."
                              " Example for disabled IPv4: <listen_host>::</listen_host>");
                      }
                      else
                      {
                          throw Exception{message, ErrorCodes::NETWORK_ERROR};
                      }
                  }
              };
  
              /// HTTP
              create_server("http_port", [&](UInt16 port)
              {
                  Poco::Net::ServerSocket socket;
                  auto address = socket_bind_listen(socket, listen_host, port);
                  socket.setReceiveTimeout(settings.http_receive_timeout);
                  socket.setSendTimeout(settings.http_send_timeout);
  
                  servers.emplace_back(std::make_unique<Poco::Net::HTTPServer>(
                      createHandlerFactory(*this, async_metrics, "HTTPHandler-factory"), server_pool, socket, http_params));
  
                  LOG_INFO(log, "Listening for http://" + address.toString());
              });
  
              /// HTTPS
              create_server("https_port", [&](UInt16 port)
              {
  #if USE_SSL
                  Poco::Net::SecureServerSocket socket;
                  auto address = socket_bind_listen(socket, listen_host, port, /* secure = */ true);
                  socket.setReceiveTimeout(settings.http_receive_timeout);
                  socket.setSendTimeout(settings.http_send_timeout);
                  servers.emplace_back(std::make_unique<Poco::Net::HTTPServer>(
                      createHandlerFactory(*this, async_metrics, "HTTPSHandler-factory"), server_pool, socket, http_params));
  
                  LOG_INFO(log, "Listening for https://" + address.toString());
  #else
                  UNUSED(port);
                  throw Exception{"HTTPS protocol is disabled because Poco library was built without NetSSL support.",
                      ErrorCodes::SUPPORT_IS_DISABLED};
  #endif
              });
  
              /// TCP
              create_server("tcp_port", [&](UInt16 port)
              {
                  Poco::Net::ServerSocket socket;
                  auto address = socket_bind_listen(socket, listen_host, port);
                  socket.setReceiveTimeout(settings.receive_timeout);
                  socket.setSendTimeout(settings.send_timeout);
                  servers.emplace_back(std::make_unique<Poco::Net::TCPServer>(
                      new TCPHandlerFactory(*this),
                      server_pool,
                      socket,
                      new Poco::Net::TCPServerParams));
  
                  LOG_INFO(log, "Listening for connections with native protocol (tcp): " + address.toString());
              });
  
              /// TCP with SSL
              create_server("tcp_port_secure", [&](UInt16 port)
              {
  #if USE_SSL
                  Poco::Net::SecureServerSocket socket;
                  auto address = socket_bind_listen(socket, listen_host, port, /* secure = */ true);
                  socket.setReceiveTimeout(settings.receive_timeout);
                  socket.setSendTimeout(settings.send_timeout);
                  servers.emplace_back(std::make_unique<Poco::Net::TCPServer>(
                      new TCPHandlerFactory(*this, /* secure= */ true),
                      server_pool,
                      socket,
                      new Poco::Net::TCPServerParams));
                  LOG_INFO(log, "Listening for connections with secure native protocol (tcp_secure): " + address.toString());
  #else
                  UNUSED(port);
                  throw Exception{"SSL support for TCP protocol is disabled because Poco library was built without NetSSL support.",
                      ErrorCodes::SUPPORT_IS_DISABLED};
  #endif
              });
  
              /// Interserver IO HTTP
              create_server("interserver_http_port", [&](UInt16 port)
              {
                  Poco::Net::ServerSocket socket;
                  auto address = socket_bind_listen(socket, listen_host, port);
                  socket.setReceiveTimeout(settings.http_receive_timeout);
                  socket.setSendTimeout(settings.http_send_timeout);
                  servers.emplace_back(std::make_unique<Poco::Net::HTTPServer>(
                      createHandlerFactory(*this, async_metrics, "InterserverIOHTTPHandler-factory"), server_pool, socket, http_params));
  
                  LOG_INFO(log, "Listening for replica communication (interserver): http://" + address.toString());
              });
  
              create_server("interserver_https_port", [&](UInt16 port)
              {
  #if USE_SSL
                  Poco::Net::SecureServerSocket socket;
                  auto address = socket_bind_listen(socket, listen_host, port, /* secure = */ true);
                  socket.setReceiveTimeout(settings.http_receive_timeout);
                  socket.setSendTimeout(settings.http_send_timeout);
                  servers.emplace_back(std::make_unique<Poco::Net::HTTPServer>(
                      createHandlerFactory(*this, async_metrics, "InterserverIOHTTPSHandler-factory"), server_pool, socket, http_params));
  
                  LOG_INFO(log, "Listening for secure replica communication (interserver): https://" + address.toString());
  #else
                  UNUSED(port);
                  throw Exception{"SSL support for TCP protocol is disabled because Poco library was built without NetSSL support.",
                          ErrorCodes::SUPPORT_IS_DISABLED};
  #endif
              });
  
              create_server("mysql_port", [&](UInt16 port)
              {
                  Poco::Net::ServerSocket socket;
                  auto address = socket_bind_listen(socket, listen_host, port, /* secure = */ true);
                  socket.setReceiveTimeout(Poco::Timespan());
                  socket.setSendTimeout(settings.send_timeout);
                  servers.emplace_back(std::make_unique<Poco::Net::TCPServer>(
                      new MySQLHandlerFactory(*this),
                      server_pool,
                      socket,
                      new Poco::Net::TCPServerParams));
  
                  LOG_INFO(log, "Listening for MySQL compatibility protocol: " + address.toString());
              });
  
              /// Prometheus (if defined and not setup yet with http_port)
              create_server("prometheus.port", [&](UInt16 port)
              {
                  Poco::Net::ServerSocket socket;
                  auto address = socket_bind_listen(socket, listen_host, port);
                  socket.setReceiveTimeout(settings.http_receive_timeout);
                  socket.setSendTimeout(settings.http_send_timeout);
                  servers.emplace_back(std::make_unique<Poco::Net::HTTPServer>(
                      createHandlerFactory(*this, async_metrics, "PrometheusHandler-factory"), server_pool, socket, http_params));
  
                  LOG_INFO(log, "Listening for Prometheus: http://" + address.toString());
              });
          }
  
          if (servers.empty())
               throw Exception("No servers started (add valid listen_host and 'tcp_port' or 'http_port' to configuration file.)", ErrorCodes::NO_ELEMENTS_IN_CONFIG);
  
          global_context->enableNamedSessions();
  
          for (auto & server : servers)
              server->start();
  
          {
              String level_str = config().getString("text_log.level", "");
              int level = level_str.empty() ? INT_MAX : Poco::Logger::parseLevel(level_str);
              setTextLog(global_context->getTextLog(), level);
          }
          buildLoggers(config(), logger());
  
          main_config_reloader->start();
          users_config_reloader->start();
          if (dns_cache_updater)
              dns_cache_updater->start();
  
          {
              std::stringstream message;
              message << "Available RAM: " << formatReadableSizeWithBinarySuffix(memory_amount) << ";"
                  << " physical cores: " << getNumberOfPhysicalCPUCores() << ";"
                  // on ARM processors it can show only enabled at current moment cores
                  << " logical cores: " << std::thread::hardware_concurrency() << ".";
              LOG_INFO(log, message.str());
          }
  
          LOG_INFO(log, "Ready for connections.");
  
          SCOPE_EXIT({
              LOG_DEBUG(log, "Received termination signal.");
              LOG_DEBUG(log, "Waiting for current connections to close.");
  
              is_cancelled = true;
  
              int current_connections = 0;
              for (auto & server : servers)
              {
                  server->stop();
                  current_connections += server->currentConnections();
              }
  
              LOG_INFO(log,
                  "Closed all listening sockets."
                      << (current_connections ? " Waiting for " + toString(current_connections) + " outstanding connections." : ""));
  
              /// Killing remaining queries.
              global_context->getProcessList().killAllQueries();
  
              if (current_connections)
              {
                  const int sleep_max_ms = 1000 * config().getInt("shutdown_wait_unfinished", 5);
                  const int sleep_one_ms = 100;
                  int sleep_current_ms = 0;
                  while (sleep_current_ms < sleep_max_ms)
                  {
                      current_connections = 0;
                      for (auto & server : servers)
                          current_connections += server->currentConnections();
                      if (!current_connections)
                          break;
                      sleep_current_ms += sleep_one_ms;
                      std::this_thread::sleep_for(std::chrono::milliseconds(sleep_one_ms));
                  }
              }
  
              LOG_INFO(
                  log, "Closed connections." << (current_connections ? " But " + toString(current_connections) + " remains."
                      " Tip: To increase wait time add to config: <shutdown_wait_unfinished>60</shutdown_wait_unfinished>" : ""));
  
              dns_cache_updater.reset();
              main_config_reloader.reset();
              users_config_reloader.reset();
  
              if (current_connections)
              {
                  /// There is no better way to force connections to close in Poco.
                  /// Otherwise connection handlers will continue to live
                  /// (they are effectively dangling objects, but they use global thread pool
                  ///  and global thread pool destructor will wait for threads, preventing server shutdown).
  
                  /// Dump coverage here, because std::atexit callback would not be called.
                  dumpCoverageReportIfPossible();
                  LOG_INFO(log, "Will shutdown forcefully.");
                  _exit(Application::EXIT_OK);
              }
          });
  
          /// try to load dictionaries immediately, throw on error and die
          ext::scope_guard dictionaries_xmls, models_xmls;
          try
          {
              if (!config().getBool("dictionaries_lazy_load", true))
              {
                  global_context->tryCreateEmbeddedDictionaries();
                  global_context->getExternalDictionariesLoader().enableAlwaysLoadEverything(true);
              }
              dictionaries_xmls = global_context->getExternalDictionariesLoader().addConfigRepository(
                  std::make_unique<ExternalLoaderXMLConfigRepository>(config(), "dictionaries_config"));
              models_xmls = global_context->getExternalModelsLoader().addConfigRepository(
                  std::make_unique<ExternalLoaderXMLConfigRepository>(config(), "models_config"));
          }
          catch (...)
          {
              LOG_ERROR(log, "Caught exception while loading dictionaries.");
              throw;
          }
  
          std::vector<std::unique_ptr<MetricsTransmitter>> metrics_transmitters;
          for (const auto & graphite_key : DB::getMultipleKeysFromConfig(config(), "", "graphite"))
          {
              metrics_transmitters.emplace_back(std::make_unique<MetricsTransmitter>(
                  global_context->getConfigRef(), graphite_key, async_metrics));
          }
  
          waitForTerminationRequest();
      }
  
      return Application::EXIT_OK;
  }
  }
  
  #pragma GCC diagnostic ignored "-Wunused-function"
  #pragma GCC diagnostic ignored "-Wmissing-declarations"
  
  int mainEntryClickHouseServer(int argc, char ** argv)
  {
      DB::Server app;
      try
      {
          return app.run(argc, argv);
      }
      catch (...)
      {
          std::cerr << DB::getCurrentExceptionMessage(true) << "\n";
          auto code = DB::getCurrentExceptionCode();
          return code ? code : 1;
      }
  }
  