Add automatic DROP DNS CACHE, update of SYSTEM queries. [#CLICKHOUSE-3645]

dbms/src/Common/ProfileEvents.cpp

@@ -138,7 +138,9 @@
     M(RWLockAcquiredReadLocks) \
     M(RWLockAcquiredWriteLocks) \
     M(RWLockReadersWaitMilliseconds) \
-    M(RWLockWritersWaitMilliseconds)
+    M(RWLockWritersWaitMilliseconds) \
+    \
+    M(NetworkErrors)
 
 namespace ProfileEvents
 {

dbms/src/Interpreters/Context.cpp

@@ -1406,9 +1406,28 @@ std::shared_ptr<Cluster> Context::tryGetCluster(const std::string & cluster_name
 
 void Context::reloadClusterConfig()
 {
-    std::lock_guard<std::mutex> lock(shared->clusters_mutex);
-    auto & config = shared->clusters_config ? *shared->clusters_config : getConfigRef();
-    shared->clusters = std::make_unique<Clusters>(config, settings);
+    while (true)
+    {
+        ConfigurationPtr cluster_config;
+        {
+            std::lock_guard<std::mutex> lock(shared->clusters_mutex);
+            cluster_config = shared->clusters_config;
+        }
+
+        auto & config = cluster_config ? *cluster_config : getConfigRef();
+        auto new_clusters = std::make_unique<Clusters>(config, settings);
+
+        {
+            std::lock_guard<std::mutex> lock(shared->clusters_mutex);
+            if (shared->clusters_config.get() == cluster_config.get())
+            {
+                shared->clusters = std::move(new_clusters);
+                return;
+            }
+
+            /// Clusters config has been suddenly changed, recompute clusters
+        }
+    }
 }
 
 

dbms/src/Interpreters/DDLWorker.cpp

@@ -39,6 +39,7 @@
 
 #include <random>
 #include <pcg_random.hpp>
+#include <Poco/Net/NetException.h>
 
 
 namespace DB
@@ -95,7 +96,7 @@ struct HostID
         {
             return DB::isLocalAddress(Poco::Net::SocketAddress(host_name, port), clickhouse_port);
         }
-        catch (const Poco::Exception & e)
+        catch (const Poco::Net::NetException & e)
         {
             /// Avoid "Host not found" exceptions
             return false;

dbms/src/Interpreters/DNSCacheUpdater.cpp

@@ -0,0 +1,116 @@
+#include "DNSCacheUpdater.h"
+#include <Common/DNSCache.h>
+#include <Interpreters/Context.h>
+#include <Storages/MergeTree/BackgroundProcessingPool.h>
+#include <Common/ProfileEvents.h>
+#include <Poco/Net/NetException.h>
+#include <common/logger_useful.h>
+
+
+namespace ProfileEvents
+{
+    extern Event NetworkErrors;
+}
+
+
+namespace DB
+{
+
+using BackgroundProcessingPoolTaskInfo = BackgroundProcessingPool::TaskInfo;
+
+namespace ErrorCodes
+{
+    extern const int TIMEOUT_EXCEEDED;
+    extern const int ALL_CONNECTION_TRIES_FAILED;
+}
+
+
+DNSCacheUpdater::DNSCacheUpdater(Context & context_)
+    : context(context_), pool(context_.getBackgroundPool())
+{
+    task_handle = pool.addTask([this] () { return run(); });
+}
+
+bool DNSCacheUpdater::run()
+{
+    /// TODO: Ensusre that we get global counter (not thread local)
+    auto num_current_network_exceptions = ProfileEvents::counters[ProfileEvents::NetworkErrors].load(std::memory_order_relaxed);
+
+    if (num_current_network_exceptions >= last_num_network_erros + min_errors_to_update_cache
+        && time(nullptr) > last_update_time + min_update_period_seconds)
+    {
+        try
+        {
+            LOG_INFO(&Poco::Logger::get("DNSCacheUpdater"), "Updating DNS cache");
+
+            DNSCache::instance().drop();
+            context.reloadClusterConfig();
+
+            last_num_network_erros = num_current_network_exceptions;
+            last_update_time = time(nullptr);
+
+            return true;
+        }
+        catch (...)
+        {
+            /// Do not increment ProfileEvents::NetworkErrors twice
+            if (isNetworkError())
+                return false;
+
+            throw;
+        }
+    }
+
+    /// According to BackgroundProcessingPool logic, if task has done work, it could be executed again immediately.
+    return false;
+}
+
+DNSCacheUpdater::~DNSCacheUpdater()
+{
+    if (task_handle)
+        pool.removeTask(task_handle);
+    task_handle.reset();
+}
+
+
+bool DNSCacheUpdater::incrementNetworkErrors()
+{
+    if (isNetworkError())
+    {
+        ProfileEvents::increment(ProfileEvents::NetworkErrors);
+        return true;
+    }
+
+    return false;
+}
+
+bool DNSCacheUpdater::isNetworkError()
+{
+    try
+    {
+        throw;
+    }
+    catch (const Exception & e)
+    {
+        if (e.code() == ErrorCodes::TIMEOUT_EXCEEDED || e.code() == ErrorCodes::ALL_CONNECTION_TRIES_FAILED)
+            return true;
+    }
+    catch (Poco::Net::DNSException & e)
+    {
+        return true;
+    }
+    catch (Poco::TimeoutException & e)
+    {
+        return true;
+    }
+    catch (...)
+    {
+        /// Do nothing
+    }
+
+    return false;
+}
+
+
+}
+

dbms/src/Interpreters/DNSCacheUpdater.h

@@ -0,0 +1,42 @@
+#pragma once
+#include <memory>
+
+
+namespace DB
+{
+
+class Context;
+class BackgroundProcessingPool;
+class BackgroundProcessingPoolTaskInfo;
+
+
+/// Add a task to BackgroundProcessingPool that watch for ProfileEvents::NetworkErrors and updates DNS cache if it has increased
+class DNSCacheUpdater
+{
+public:
+
+    DNSCacheUpdater(Context & context);
+    ~DNSCacheUpdater();
+
+    /// Call it inside catch section
+    /// Returns true if it is a network error
+    static bool isNetworkError();
+
+    /// Checks if it is a network error and increments ProfileEvents::NetworkErrors
+    static bool incrementNetworkErrors();
+
+private:
+    bool run();
+
+    Context & context;
+    BackgroundProcessingPool & pool;
+    std::shared_ptr<BackgroundProcessingPoolTaskInfo> task_handle;
+    size_t last_num_network_erros = 0;
+    time_t last_update_time = 0;
+
+    static constexpr size_t min_errors_to_update_cache = 3;
+    static constexpr time_t min_update_period_seconds = 10;
+};
+
+
+}

dbms/src/Interpreters/InterpreterSystemQuery.cpp

@@ -63,6 +63,10 @@ BlockIO InterpreterSystemQuery::execute()
 
     using Type = ASTSystemQuery::Type;
 
+    /// Use global context with fresh system profile settings
+    Context system_context = context.getGlobalContext();
+    system_context.setSetting("profile", context.getSystemProfileName());
+
     switch (query.type)
     {
         case Type::SHUTDOWN:
@@ -76,29 +80,32 @@ BlockIO InterpreterSystemQuery::execute()
         case Type::DROP_DNS_CACHE:
             DNSCache::instance().drop();
             /// Reinitialize clusters to update their resolved_addresses
-            context.reloadClusterConfig();
+            system_context.reloadClusterConfig();
             break;
         case Type::DROP_MARK_CACHE:
-            context.dropMarkCache();
+            system_context.dropMarkCache();
             break;
         case Type::DROP_UNCOMPRESSED_CACHE:
-            context.dropUncompressedCache();
+            system_context.dropUncompressedCache();
             break;
         case Type::RELOAD_DICTIONARY:
-            context.getExternalDictionaries().reloadDictionary(query.target_dictionary);
+            system_context.getExternalDictionaries().reloadDictionary(query.target_dictionary);
             break;
         case Type::RELOAD_DICTIONARIES:
         {
             auto status = getOverallExecutionStatusOfCommands(
-                    [&] { context.getExternalDictionaries().reload(); },
-                    [&] { context.getEmbeddedDictionaries().reload(); }
+                    [&] { system_context.getExternalDictionaries().reload(); },
+                    [&] { system_context.getEmbeddedDictionaries().reload(); }
             );
             if (status.code != 0)
                 throw Exception(status.message, status.code);
             break;
         }
+        case Type::RELOAD_EMBEDDED_DICTIONARIES:
+            system_context.getEmbeddedDictionaries().reload();
+            break;
         case Type::RELOAD_CONFIG:
-            context.reloadConfig();
+            system_context.reloadConfig();
             break;
         case Type::STOP_LISTEN_QUERIES:
         case Type::START_LISTEN_QUERIES:

dbms/src/Interpreters/executeQuery.cpp

@@ -23,6 +23,7 @@
 #include <Interpreters/ProcessList.h>
 #include <Interpreters/QueryLog.h>
 #include <Interpreters/executeQuery.h>
+#include "DNSCacheUpdater.h"
 
 
 namespace ProfileEvents
@@ -377,6 +378,8 @@ static std::tuple<ASTPtr, BlockIO> executeQueryImpl(
         if (!internal)
             onExceptionBeforeStart(query, context, current_time);
 
+        DNSCacheUpdater::incrementNetworkErrors();
+
         throw;
     }
 

dbms/src/Parsers/ASTSystemQuery.cpp

@@ -39,6 +39,8 @@ const char * ASTSystemQuery::typeToString(Type type)
             return "RELOAD DICTIONARY";
         case Type::RELOAD_DICTIONARIES:
             return "RELOAD DICTIONARIES";
+        case Type::RELOAD_EMBEDDED_DICTIONARIES:
+            return "RELOAD EMBEDDED DICTIONARIES";
         case Type::RELOAD_CONFIG:
             return "RELOAD CONFIG";
         case Type::STOP_MERGES:

dbms/src/Parsers/ASTSystemQuery.h

@@ -24,6 +24,7 @@ public:
         SYNC_REPLICA,
         RELOAD_DICTIONARY,
         RELOAD_DICTIONARIES,
+        RELOAD_EMBEDDED_DICTIONARIES,
         RELOAD_CONFIG,
         STOP_MERGES,
         START_MERGES,

dbms/src/Server/Server.cpp

@@ -40,6 +40,9 @@
 #if Poco_NetSSL_FOUND
 #include <Poco/Net/Context.h>
 #include <Poco/Net/SecureServerSocket.h>
+#include <Interpreters/DNSCacheUpdater.h>
+
+
 #endif
 
 namespace CurrentMetrics
@@ -322,6 +325,9 @@ int Server::main(const std::vector<std::string> & /*args*/)
         global_context->setDDLWorker(std::make_shared<DDLWorker>(ddl_zookeeper_path, *global_context, &config(), "distributed_ddl"));
     }
 
+    /// Initialize a watcher updating DNS cache in case of network errors
+    DNSCacheUpdater dns_cache_updater(*global_context);
+
     {
         Poco::Timespan keep_alive_timeout(config().getUInt("keep_alive_timeout", 10), 0);
 

dbms/src/Storages/MergeTree/BackgroundProcessingPool.cpp

@@ -6,6 +6,7 @@
 #include <IO/WriteHelpers.h>
 #include <common/logger_useful.h>
 #include <Storages/MergeTree/BackgroundProcessingPool.h>
+#include <Interpreters/DNSCacheUpdater.h>
 
 #include <pcg_random.hpp>
 #include <random>
@@ -25,7 +26,7 @@ constexpr double BackgroundProcessingPool::sleep_seconds;
 constexpr double BackgroundProcessingPool::sleep_seconds_random_part;
 
 
-void BackgroundProcessingPool::TaskInfo::wake()
+void BackgroundProcessingPoolTaskInfo::wake()
 {
     if (removed)
         return;
@@ -36,7 +37,7 @@ void BackgroundProcessingPool::TaskInfo::wake()
         std::unique_lock<std::mutex> lock(pool.tasks_mutex);
 
         auto next_time_to_execute = iterator->first;
-        TaskHandle this_task_handle = iterator->second;
+        auto this_task_handle = iterator->second;
 
         /// If this task was done nothing at previous time and it has to sleep, then cancel sleep time.
         if (next_time_to_execute > current_time)
@@ -180,6 +181,7 @@ void BackgroundProcessingPool::threadFunction()
         catch (...)
         {
             tryLogCurrentException(__PRETTY_FUNCTION__);
+            DNSCacheUpdater::incrementNetworkErrors();
         }
 
         if (shutdown)

dbms/src/Storages/MergeTree/BackgroundProcessingPool.h

@@ -16,6 +16,9 @@
 namespace DB
 {
 
+class BackgroundProcessingPool;
+class BackgroundProcessingPoolTaskInfo;
+
 /** Using a fixed number of threads, perform an arbitrary number of tasks in an infinite loop.
   * In this case, one task can run simultaneously from different threads.
   * Designed for tasks that perform continuous background work (for example, merge).
@@ -27,29 +30,7 @@ class BackgroundProcessingPool
 public:
     /// Returns true, if some useful work was done. In that case, thread will not sleep before next run of this task.
     using Task = std::function<bool()>;
-
-
-    class TaskInfo
-    {
-    public:
-        /// Wake up any thread.
-        void wake();
-
-        TaskInfo(BackgroundProcessingPool & pool_, const Task & function_) : pool(pool_), function(function_) {}
-
-    private:
-        friend class BackgroundProcessingPool;
-
-        BackgroundProcessingPool & pool;
-        Task function;
-
-        /// Read lock is hold when task is executed.
-        std::shared_mutex rwlock;
-        std::atomic<bool> removed {false};
-
-        std::multimap<Poco::Timestamp, std::shared_ptr<TaskInfo>>::iterator iterator;
-    };
-
+    using TaskInfo = BackgroundProcessingPoolTaskInfo;
     using TaskHandle = std::shared_ptr<TaskInfo>;
 
 
@@ -65,7 +46,9 @@ public:
 
     ~BackgroundProcessingPool();
 
-private:
+protected:
+    friend class BackgroundProcessingPoolTaskInfo;
+
     using Tasks = std::multimap<Poco::Timestamp, TaskHandle>;    /// key is desired next time to execute (priority).
     using Threads = std::vector<std::thread>;
 
@@ -87,4 +70,27 @@ private:
 
 using BackgroundProcessingPoolPtr = std::shared_ptr<BackgroundProcessingPool>;
 
+
+class BackgroundProcessingPoolTaskInfo
+{
+public:
+    /// Wake up any thread.
+    void wake();
+
+    BackgroundProcessingPoolTaskInfo(BackgroundProcessingPool & pool_, const BackgroundProcessingPool::Task & function_)
+        : pool(pool_), function(function_) {}
+
+protected:
+    friend class BackgroundProcessingPool;
+
+    BackgroundProcessingPool & pool;
+    BackgroundProcessingPool::Task function;
+
+    /// Read lock is hold when task is executed.
+    std::shared_mutex rwlock;
+    std::atomic<bool> removed {false};
+
+    std::multimap<Poco::Timestamp, std::shared_ptr<BackgroundProcessingPoolTaskInfo>>::iterator iterator;
+};
+
 }

dbms/tests/integration/test_system_queries/test.py

@@ -58,6 +58,7 @@ def test_DROP_DNS_CACHE(started_cluster):
     instance = cluster.instances['ch1']
 
     instance.exec_in_container(['bash', '-c', 'echo 127.255.255.255 lost_host > /etc/hosts'], privileged=True, user='root')
+    instance.query("SYSTEM DROP DNS CACHE")
 
     with pytest.raises(QueryRuntimeException):
         instance.query("SELECT * FROM remote('lost_host', 'system', 'one')")
@@ -74,6 +75,22 @@ def test_DROP_DNS_CACHE(started_cluster):
     assert TSV(instance.query("SELECT DISTINCT host_name, host_address FROM system.clusters WHERE cluster='lost_host_cluster'")) == TSV("lost_host\t127.0.0.1\n")
 
 
+def test_automatic_DROP_DNS_CACHE(started_cluster):
+    instance = cluster.instances['ch1']
+
+    instance.exec_in_container(['bash', '-c', 'echo 127.255.255.255 lost_host > /etc/hosts'], privileged=True, user='root')
+    instance.query("SYSTEM DROP DNS CACHE")
+
+    for i in xrange(5):
+        with pytest.raises(QueryRuntimeException):
+            instance.query("SELECT * FROM remote('lost_host', 'system', 'one')")
+
+    time.sleep(20)
+
+    # DNS cache should be automatically updated after this delay
+    instance.query("SELECT * FROM remote('lost_host', 'system', 'one')")
+
+
 def test_RELOAD_CONFIG_AND_MACROS(started_cluster):
 
     macros = "<yandex><macros><mac>ro</mac></macros></yandex>"