Better

src/Common/MemoryTracker.h

@@ -62,8 +62,8 @@ private:
     void logMemoryUsage(Int64 current) const;
 
 public:
-    MemoryTracker(VariableContext level_ = VariableContext::Thread);
-    MemoryTracker(MemoryTracker * parent_, VariableContext level_ = VariableContext::Thread);
+    explicit MemoryTracker(VariableContext level_ = VariableContext::Thread);
+    explicit MemoryTracker(MemoryTracker * parent_, VariableContext level_ = VariableContext::Thread);
 
     ~MemoryTracker();
 

src/Interpreters/Context.cpp

@@ -2729,19 +2729,21 @@ PartUUIDsPtr Context::getIgnoredPartUUIDs() const
 
 void Context::initializeBackgroundExecutors()
 {
+    // Initialize background executors with callbacks to be able to change pool size and tasks count at runtime.
+
     shared->merge_mutate_executor = MergeTreeBackgroundExecutor::create
     (
         MergeTreeBackgroundExecutor::Type::MERGE_MUTATE,
-        [this] () { return getSettingsRef().background_pool_size; },
-        [this] () { return getSettingsRef().background_pool_size; },
+        [this] () { auto lock = getLock(); return getSettingsRef().background_pool_size; },
+        [this] () { auto lock = getLock(); return getSettingsRef().background_pool_size; },
         CurrentMetrics::BackgroundPoolTask
     );
 
     shared->moves_executor = MergeTreeBackgroundExecutor::create
     (
         MergeTreeBackgroundExecutor::Type::MOVE,
-        [this] () { return getSettingsRef().background_move_pool_size; },
-        [this] () { return getSettingsRef().background_move_pool_size; },
+        [this] () { auto lock = getLock(); return getSettingsRef().background_move_pool_size; },
+        [this] () { auto lock = getLock(); return getSettingsRef().background_move_pool_size; },
         CurrentMetrics::BackgroundMovePoolTask
     );
 
@@ -2749,8 +2751,8 @@ void Context::initializeBackgroundExecutors()
     shared->fetch_executor = MergeTreeBackgroundExecutor::create
     (
         MergeTreeBackgroundExecutor::Type::FETCH,
-        [this] () { return getSettingsRef().background_fetches_pool_size; },
-        [this] () { return getSettingsRef().background_fetches_pool_size; },
+        [this] () { auto lock = getLock(); return getSettingsRef().background_fetches_pool_size; },
+        [this] () { auto lock = getLock(); return getSettingsRef().background_fetches_pool_size; },
         CurrentMetrics::BackgroundFetchesPoolTask
     );
 }

src/Storages/MergeTree/BackgroundJobsAssignee.cpp

@@ -85,7 +85,7 @@ void BackgroundJobsAssignee::start()
 {
     std::lock_guard lock(holder_mutex);
     if (!holder)
-        holder = getContext()->getSchedulePool().createTask("BackgroundJobsAssignee:" + toString(type), [this]{ main(); });
+        holder = getContext()->getSchedulePool().createTask("BackgroundJobsAssignee:" + toString(type), [this]{ threadFunc(); });
 
     holder->activateAndSchedule();
 }
@@ -106,7 +106,7 @@ void BackgroundJobsAssignee::finish()
 }
 
 
-void BackgroundJobsAssignee::main()
+void BackgroundJobsAssignee::threadFunc()
 try
 {
     bool succeed = false;

src/Storages/MergeTree/BackgroundJobsAssignee.h

@@ -29,7 +29,7 @@ struct ExecutableTaskSchedulingSettings
 
 class MergeTreeData;
 
-class BackgroundJobsAssignee : protected WithContext
+class BackgroundJobsAssignee : public WithContext
 {
 private:
     MergeTreeData & data;
@@ -49,6 +49,7 @@ private:
     std::mutex holder_mutex;
 
 public:
+    ///
     enum class Type
     {
         DataProcessing,
@@ -77,7 +78,7 @@ private:
     static String toString(Type type);
 
     /// Function that executes in background scheduling pool
-    void main();
+    void threadFunc();
 };
 
 

src/Storages/MergeTree/IExecutableTask.h

@@ -9,10 +9,21 @@
 namespace DB
 {
 
+/**
+ * Generic interface for background operations. Simply this is self-made coroutine.
+ * The main method is executeStep, which will return true
+ * if the task wants to execute another 'step' in near future and false otherwise.
+ *
+ * Each storage assigns some operations such as merges, mutations, fetches, etc.
+ * We need to ask a storage or some another entity to try to assign another operation when current operation is completed.
+ *
+ * Each task corresponds to a storage, that's why there is a method getStorageID.
+ * This is needed to correctly shutdown a storage, e.g. we need to wait for all background operations to complete.
+ */
 class IExecutableTask
 {
 public:
-    virtual bool execute() = 0;
+    virtual bool executeStep() = 0;
     virtual void onCompleted() = 0;
     virtual StorageID getStorageID() = 0;
     virtual ~IExecutableTask() = default;
@@ -21,29 +32,37 @@ public:
 using ExecutableTaskPtr = std::shared_ptr<IExecutableTask>;
 
 
-class LambdaAdapter : public shared_ptr_helper<LambdaAdapter>, public IExecutableTask
+/**
+ * Some background operations won't represent a coroutines (don't want to be executed step-by-step). For this we have this wrapper.
+ */
+class ExecutableLambdaAdapter : public shared_ptr_helper<ExecutableLambdaAdapter>, public IExecutableTask
 {
 public:
 
-    template <typename InnerJob, typename Callback>
-    explicit LambdaAdapter(InnerJob && inner_, Callback && callback_, StorageID id_)
-        : inner(inner_), callback(callback_), id(id_) {}
+    template <typename Job, typename Callback>
+    explicit ExecutableLambdaAdapter(
+        Job && job_to_execute_,
+        Callback && job_result_callback_,
+        StorageID id_)
+        : job_to_execute(job_to_execute_)
+        , job_result_callback(job_result_callback_)
+        , id(id_) {}
 
-    bool execute() override
+    bool executeStep() override
     {
-        res = inner();
-        inner = {};
+        res = job_to_execute();
+        job_to_execute = {};
         return false;
     }
 
-    void onCompleted() override { callback(!res); }
+    void onCompleted() override { job_result_callback(!res); }
 
     StorageID getStorageID() override { return id; }
 
 private:
     bool res = false;
-    std::function<bool()> inner;
-    std::function<void(bool)> callback;
+    std::function<bool()> job_to_execute;
+    std::function<void(bool)> job_result_callback;
     StorageID id;
 };
 

src/Storages/MergeTree/MergeTreeBackgroundExecutor.cpp

@@ -39,6 +39,9 @@ void MergeTreeBackgroundExecutor::updateConfiguration()
         pool.setMaxThreads(new_threads_count);
         pool.setQueueSize(new_max_tasks_count);
 
+        std::cout << "threads_count " << threads_count << std::endl;
+
+        /// We don't enter this loop if size is decreased.
         for (size_t number = threads_count; number < new_threads_count; ++number)
             pool.scheduleOrThrowOnError([this, number] { threadFunction(number); });
     }
@@ -74,6 +77,8 @@ bool MergeTreeBackgroundExecutor::trySchedule(ExecutableTaskPtr task)
     try
     {
         /// This is needed to increase / decrease the number of threads at runtime
+        /// Using stopwatch here not to do it so often.
+        /// No need to move the time to a config.
         if (update_timer.compareAndRestartDeferred(10.))
             updateConfiguration();
     }
@@ -86,7 +91,7 @@ bool MergeTreeBackgroundExecutor::trySchedule(ExecutableTaskPtr task)
     if (value.load() >= static_cast<int64_t>(max_tasks_count))
         return false;
 
-    pending.push_back(std::make_shared<Item>(std::move(task), metric));
+    pending.push_back(std::make_shared<TaskRuntimeData>(std::move(task), metric));
 
     has_tasks.notify_one();
     return true;
@@ -95,7 +100,7 @@ bool MergeTreeBackgroundExecutor::trySchedule(ExecutableTaskPtr task)
 
 void MergeTreeBackgroundExecutor::removeTasksCorrespondingToStorage(StorageID id)
 {
-    std::vector<ItemPtr> tasks_to_wait;
+    std::vector<TaskRuntimeDataPtr> tasks_to_wait;
     {
         std::lock_guard lock(mutex);
 
@@ -118,7 +123,7 @@ void MergeTreeBackgroundExecutor::removeTasksCorrespondingToStorage(StorageID id
 }
 
 
-void MergeTreeBackgroundExecutor::routine(ItemPtr item)
+void MergeTreeBackgroundExecutor::routine(TaskRuntimeDataPtr item)
 {
     auto erase_from_active = [this, item]
     {
@@ -127,7 +132,7 @@ void MergeTreeBackgroundExecutor::routine(ItemPtr item)
 
     try
     {
-        if (item->task->execute())
+        if (item->task->executeStep())
         {
             std::lock_guard guard(mutex);
 
@@ -143,9 +148,12 @@ void MergeTreeBackgroundExecutor::routine(ItemPtr item)
             return;
         }
 
-        std::lock_guard guard(mutex);
-        erase_from_active();
-        has_tasks.notify_one();
+        {
+            std::lock_guard guard(mutex);
+            erase_from_active();
+            has_tasks.notify_one();
+        }
+
         /// In a situation of a lack of memory this method can throw an exception,
         /// because it may interact somehow with BackgroundSchedulePool, which may allocate memory
         /// But it is rather safe, because we have try...catch block here, and another one in ThreadPool.
@@ -170,11 +178,12 @@ void MergeTreeBackgroundExecutor::threadFunction(size_t number)
 
     while (true)
     {
-        ItemPtr item;
+        TaskRuntimeDataPtr item;
         {
             std::unique_lock lock(mutex);
             has_tasks.wait(lock, [this](){ return !pending.empty() || shutdown; });
 
+            /// Decrease the number of threads (setting could be dynamically reloaded)
             if (number >= threads_count)
                 break;
 

src/Storages/MergeTree/MergeTreeBackgroundExecutor.h

@@ -25,15 +25,25 @@ namespace DB
  *  It can execute only successors of ExecutableTask interface.
  *  Which is a self-written coroutine. It suspends, when returns true from execute() method.
  *
- *  Executor consists of ThreadPool to execute pieces of a task (basically calls 'execute' on a task)
- *  and a scheduler thread, which manages the tasks. Due to bad experience of working with high memory under
- *  high memory pressure scheduler thread mustn't do any allocations,
- *  because it will be a fatal error if this thread will die from a random exception.
- *
  *  There are two queues of a tasks: pending (main queue for all the tasks) and active (currently executing).
+ *  Pending queue is needed since the number of tasks will be more than thread to execute.
+ *  Pending tasks are tasks that successfully scheduled to an executor or tasks that have some extra steps to execute.
  *  There is an invariant, that task may occur only in one of these queue. It can occur in both queues only in critical sections.
  *
- *  Due to all caveats I described above we use boost::circular_buffer as a container for queues.
+ *  Pending:                                              Active:
+ *
+ *  |s| |s| |s| |s| |s| |s| |s| |s| |s| |s|               |s|
+ *  |s| |s| |s| |s| |s| |s| |s| |s| |s|                   |s|
+ *  |s| |s|     |s|     |s| |s|     |s|                   |s|
+ *      |s|             |s| |s|                           |s|
+ *      |s|                 |s|
+ *                          |s|
+ *
+ *  Each task is simply a sequence of steps. Heavier tasks have longer sequences.
+ *  When a step of a task is executed, we move tasks to pending queue. And take another from the queue's head.
+ *  With these architecture all small merges / mutations will be executed faster, than bigger ones.
+ *
+ *  We use boost::circular_buffer as a container for queues not to do any allocations.
  *
  *  Another nuisance that we faces with is than background operations always interact with an associated Storage.
  *  So, when a Storage want to shutdown, it must wait until all its background operaions are finished.
@@ -43,7 +53,6 @@ class MergeTreeBackgroundExecutor : public shared_ptr_helper<MergeTreeBackground
 public:
 
     using CountGetter = std::function<size_t()>;
-    using Callback = std::function<void()>;
 
     enum class Type
     {
@@ -107,13 +116,16 @@ private:
 
     AtomicStopwatch update_timer;
 
-    struct Item
+    /**
+     * Has RAII class to determine how many tasks are waiting for the execution and executing at the moment.
+     * Also has some flags and primitives to wait for current task to be executed.
+     */
+    struct TaskRuntimeData
     {
-        explicit Item(ExecutableTaskPtr && task_, CurrentMetrics::Metric metric_)
+        TaskRuntimeData(ExecutableTaskPtr && task_, CurrentMetrics::Metric metric_)
             : task(std::move(task_))
             , increment(std::move(metric_))
-        {
-        }
+        {}
 
         ExecutableTaskPtr task;
         CurrentMetrics::Increment increment;
@@ -124,14 +136,16 @@ private:
         Poco::Event is_done{/*autoreset=*/false};
     };
 
-    using ItemPtr = std::shared_ptr<Item>;
+    using TaskRuntimeDataPtr = std::shared_ptr<TaskRuntimeData>;
 
-    void routine(ItemPtr item);
+    void routine(TaskRuntimeDataPtr item);
+
+    /// Number all the threads in ThreadPool. To be able to lower the number of threads in runtime.
     void threadFunction(size_t number);
 
     /// Initially it will be empty
-    boost::circular_buffer<ItemPtr> pending{0};
-    boost::circular_buffer<ItemPtr> active{0};
+    boost::circular_buffer<TaskRuntimeDataPtr> pending{0};
+    boost::circular_buffer<TaskRuntimeDataPtr> active{0};
 
     std::mutex mutex;
     std::condition_variable has_tasks;

src/Storages/MergeTree/MergeTreeData.cpp

@@ -200,8 +200,8 @@ MergeTreeData::MergeTreeData(
     , data_parts_by_info(data_parts_indexes.get<TagByInfo>())
     , data_parts_by_state_and_info(data_parts_indexes.get<TagByStateAndInfo>())
     , parts_mover(this)
-    , background_executor(*this, BackgroundJobsAssignee::Type::DataProcessing, getContext())
-    , background_moves_executor(*this, BackgroundJobsAssignee::Type::Moving, getContext())
+    , background_operations_assignee(*this, BackgroundJobsAssignee::Type::DataProcessing, getContext())
+    , background_moves_assignee(*this, BackgroundJobsAssignee::Type::Moving, getContext())
 {
     const auto settings = getSettings();
     allow_nullable_key = attach || settings->allow_nullable_key;
@@ -311,17 +311,17 @@ MergeTreeData::MergeTreeData(
     common_assignee_trigger = [this] (bool delay) noexcept
     {
         if (delay)
-            background_executor.postpone();
+            background_operations_assignee.postpone();
         else
-            background_executor.trigger();
+            background_operations_assignee.trigger();
     };
 
     moves_assignee_trigger = [this] (bool delay) noexcept
     {
         if (delay)
-            background_moves_executor.postpone();
+            background_moves_assignee.postpone();
         else
-            background_moves_executor.trigger();
+            background_moves_assignee.trigger();
     };
 }
 
@@ -5029,7 +5029,7 @@ MergeTreeData::CurrentlyMovingPartsTagger::~CurrentlyMovingPartsTagger()
     }
 }
 
-bool MergeTreeData::scheduleDataMovingJob(BackgroundJobsAssignee & executor)
+bool MergeTreeData::scheduleDataMovingJob(BackgroundJobsAssignee & assignee)
 {
     if (parts_mover.moves_blocker.isCancelled())
         return false;
@@ -5038,7 +5038,7 @@ bool MergeTreeData::scheduleDataMovingJob(BackgroundJobsAssignee & executor)
     if (moving_tagger->parts_to_move.empty())
         return false;
 
-    executor.scheduleMoveTask(LambdaAdapter::create(
+    assignee.scheduleMoveTask(ExecutableLambdaAdapter::create(
         [this, moving_tagger] () mutable
         {
             return moveParts(moving_tagger);

src/Storages/MergeTree/MergeTreeData.h

@@ -827,9 +827,9 @@ public:
     PinnedPartUUIDsPtr getPinnedPartUUIDs() const;
 
     /// Schedules background job to like merge/mutate/fetch an executor
-    virtual bool scheduleDataProcessingJob(BackgroundJobsAssignee & executor) = 0;
+    virtual bool scheduleDataProcessingJob(BackgroundJobsAssignee & assignee) = 0;
     /// Schedules job to move parts between disks/volumes and so on.
-    bool scheduleDataMovingJob(BackgroundJobsAssignee & executor);
+    bool scheduleDataMovingJob(BackgroundJobsAssignee & assignee);
     bool areBackgroundMovesNeeded() const;
 
     /// Lock part in zookeeper for shared data in several nodes
@@ -925,10 +925,18 @@ protected:
 
     /// Executors are common for both ReplicatedMergeTree and plain MergeTree
     /// but they are being started and finished in derived classes, so let them be protected.
-    BackgroundJobsAssignee background_executor;
-    BackgroundJobsAssignee background_moves_executor;
+    ///
+    /// Why there are two executors, not one? Or an executor for each kind of operation?
+    /// It is historically formed.
+    /// Another explanation is that moving operations are common for Replicated and Plain MergeTree classes.
+    /// Task that schedules this operations is executed with its own timetable and triggered in a specific places in code.
+    /// And for ReplicatedMergeTree we don't have LogEntry type for this operation.
+    BackgroundJobsAssignee background_operations_assignee;
+    BackgroundJobsAssignee background_moves_assignee;
 
+    /// Strongly connected with two fields above.
     /// Every task that is finished will ask to assign a new one into an executor.
+    /// These callbacks will be passed to the constructor of each task.
     std::function<void(bool)> common_assignee_trigger;
     std::function<void(bool)> moves_assignee_trigger;
 

src/Storages/MergeTree/MergeTreeSink.cpp

@@ -37,7 +37,7 @@ void MergeTreeSink::consume(Chunk chunk)
             PartLog::addNewPart(storage.getContext(), part, watch.elapsed());
 
             /// Initiate async merge - it will be done if it's good time for merge and if there are space in 'background_pool'.
-            storage.background_executor.trigger();
+            storage.background_operations_assignee.trigger();
         }
     }
 }

src/Storages/MergeTree/ReplicatedMergeTreeQueue.cpp

@@ -624,7 +624,7 @@ int32_t ReplicatedMergeTreeQueue::pullLogsToQueue(zkutil::ZooKeeperPtr zookeeper
             }
         }
 
-        storage.background_executor.trigger();
+        storage.background_operations_assignee.trigger();
     }
 
     return stat.version;
@@ -713,7 +713,7 @@ void ReplicatedMergeTreeQueue::updateMutations(zkutil::ZooKeeperPtr zookeeper, C
     }
 
     if (some_active_mutations_were_killed)
-        storage.background_executor.trigger();
+        storage.background_operations_assignee.trigger();
 
     if (!entries_to_load.empty())
     {
@@ -847,7 +847,7 @@ ReplicatedMergeTreeMutationEntryPtr ReplicatedMergeTreeQueue::removeMutation(
     }
 
     if (mutation_was_active)
-        storage.background_executor.trigger();
+        storage.background_operations_assignee.trigger();
 
     return entry;
 }

src/Storages/MergeTree/ReplicatedMergeTreeRestartingThread.cpp

@@ -204,7 +204,7 @@ bool ReplicatedMergeTreeRestartingThread::tryStartup()
         storage.partial_shutdown_event.reset();
 
         /// Start queue processing
-        storage.background_executor.start();
+        storage.background_operations_assignee.start();
 
         storage.queue_updating_task->activateAndSchedule();
         storage.mutations_updating_task->activateAndSchedule();
@@ -389,7 +389,7 @@ void ReplicatedMergeTreeRestartingThread::partialShutdown()
         auto fetch_lock = storage.fetcher.blocker.cancel();
         auto merge_lock = storage.merger_mutator.merges_blocker.cancel();
         auto move_lock = storage.parts_mover.moves_blocker.cancel();
-        storage.background_executor.finish();
+        storage.background_operations_assignee.finish();
     }
 
     LOG_TRACE(log, "Threads finished");

src/Storages/MergeTree/tests/gtest_executor.cpp

@@ -24,7 +24,7 @@ public:
     {
     }
 
-    bool execute() override
+    bool executeStep() override
     {
         auto sleep_time = distribution(generator);
         std::this_thread::sleep_for(std::chrono::milliseconds(5 * sleep_time));

src/Storages/StorageMergeTree.cpp

@@ -112,7 +112,7 @@ void StorageMergeTree::startup()
 
     try
     {
-        background_executor.start();
+        background_operations_assignee.start();
         startBackgroundMovesIfNeeded();
     }
     catch (...)
@@ -150,8 +150,8 @@ void StorageMergeTree::shutdown()
     merger_mutator.merges_blocker.cancelForever();
     parts_mover.moves_blocker.cancelForever();
 
-    background_executor.finish();
-    background_moves_executor.finish();
+    background_operations_assignee.finish();
+    background_moves_assignee.finish();
 
     try
     {
@@ -411,7 +411,7 @@ Int64 StorageMergeTree::startMutation(const MutationCommands & commands, String
 
         LOG_INFO(log, "Added mutation: {}", mutation_file_name);
     }
-    background_executor.trigger();
+    background_operations_assignee.trigger();
     return version;
 }
 
@@ -637,7 +637,7 @@ CancellationCode StorageMergeTree::killMutation(const String & mutation_id)
     }
 
     /// Maybe there is another mutation that was blocked by the killed one. Try to execute it immediately.
-    background_executor.trigger();
+    background_operations_assignee.trigger();
 
     return CancellationCode::CancelSent;
 }
@@ -1041,7 +1041,7 @@ bool StorageMergeTree::mutateSelectedPart(const StorageMetadataPtr & metadata_sn
     return true;
 }
 
-bool StorageMergeTree::scheduleDataProcessingJob(BackgroundJobsAssignee & executor) //-V657
+bool StorageMergeTree::scheduleDataProcessingJob(BackgroundJobsAssignee & assignee) //-V657
 {
     if (shutdown_called)
         return false;
@@ -1073,7 +1073,7 @@ bool StorageMergeTree::scheduleDataProcessingJob(BackgroundJobsAssignee & execut
 
     if (merge_entry)
     {
-        executor.scheduleMergeMutateTask(LambdaAdapter::create(
+        assignee.scheduleMergeMutateTask(ExecutableLambdaAdapter::create(
             [this, metadata_snapshot, merge_entry, share_lock] () mutable
             {
                 return mergeSelectedParts(metadata_snapshot, false, {}, *merge_entry, share_lock);
@@ -1082,27 +1082,27 @@ bool StorageMergeTree::scheduleDataProcessingJob(BackgroundJobsAssignee & execut
     }
     if (mutate_entry)
     {
-        executor.scheduleMergeMutateTask(LambdaAdapter::create(
+        assignee.scheduleMergeMutateTask(ExecutableLambdaAdapter::create(
             [this, metadata_snapshot, merge_entry, mutate_entry, share_lock] () mutable
             {
             return mutateSelectedPart(metadata_snapshot, *mutate_entry, share_lock);
             }, common_assignee_trigger, getStorageID()));
         return true;
     }
-    bool executed = false;
+    bool scheduled = false;
     if (time_after_previous_cleanup_temporary_directories.compareAndRestartDeferred(getContext()->getSettingsRef().merge_tree_clear_old_temporary_directories_interval_seconds))
     {
-        executor.scheduleMergeMutateTask(LambdaAdapter::create(
+        assignee.scheduleMergeMutateTask(ExecutableLambdaAdapter::create(
             [this, share_lock] ()
             {
                 clearOldTemporaryDirectories(getSettings()->temporary_directories_lifetime.totalSeconds());
                 return true;
             }, common_assignee_trigger, getStorageID()));
-        executed = true;
+        scheduled = true;
     }
     if (time_after_previous_cleanup_parts.compareAndRestartDeferred(getContext()->getSettingsRef().merge_tree_clear_old_parts_interval_seconds))
     {
-        executor.scheduleMergeMutateTask(LambdaAdapter::create(
+        assignee.scheduleMergeMutateTask(ExecutableLambdaAdapter::create(
             [this, share_lock] ()
             {
                 /// All use relative_data_path which changes during rename
@@ -1113,10 +1113,10 @@ bool StorageMergeTree::scheduleDataProcessingJob(BackgroundJobsAssignee & execut
                 clearEmptyParts();
                 return true;
             }, common_assignee_trigger, getStorageID()));
-        executed = true;
+        scheduled = true;
      }
 
-    return executed;
+    return scheduled;
 }
 
 Int64 StorageMergeTree::getCurrentMutationVersion(
@@ -1567,9 +1567,9 @@ ActionLock StorageMergeTree::getActionLock(StorageActionBlockType action_type)
 void StorageMergeTree::onActionLockRemove(StorageActionBlockType action_type)
 {
     if (action_type == ActionLocks::PartsMerge ||  action_type == ActionLocks::PartsTTLMerge)
-        background_executor.trigger();
+        background_operations_assignee.trigger();
     else if (action_type == ActionLocks::PartsMove)
-        background_moves_executor.trigger();
+        background_moves_assignee.trigger();
 }
 
 CheckResults StorageMergeTree::checkData(const ASTPtr & query, ContextPtr local_context)
@@ -1647,7 +1647,7 @@ MutationCommands StorageMergeTree::getFirstAlterMutationCommandsForPart(const Da
 void StorageMergeTree::startBackgroundMovesIfNeeded()
 {
     if (areBackgroundMovesNeeded())
-        background_moves_executor.start();
+        background_moves_assignee.start();
 }
 
 std::unique_ptr<MergeTreeSettings> StorageMergeTree::getDefaultSettings() const

src/Storages/StorageMergeTree.h

@@ -95,7 +95,7 @@ public:
 
     RestoreDataTasks restoreFromBackup(const BackupPtr & backup, const String & data_path_in_backup, const ASTs & partitions, ContextMutablePtr context) override;
 
-    bool scheduleDataProcessingJob(BackgroundJobsAssignee & executor) override;
+    bool scheduleDataProcessingJob(BackgroundJobsAssignee & assignee) override;
 
     MergeTreeDeduplicationLog * getDeduplicationLog() { return deduplication_log.get(); }
 

src/Storages/StorageReplicatedMergeTree.cpp

@@ -3173,7 +3173,7 @@ bool StorageReplicatedMergeTree::processQueueEntry(ReplicatedMergeTreeQueue::Sel
     });
 }
 
-bool StorageReplicatedMergeTree::scheduleDataProcessingJob(BackgroundJobsAssignee & executor)
+bool StorageReplicatedMergeTree::scheduleDataProcessingJob(BackgroundJobsAssignee & assignee)
 {
     /// If replication queue is stopped exit immediately as we successfully executed the task
     if (queue.actions_blocker.isCancelled())
@@ -3188,7 +3188,7 @@ bool StorageReplicatedMergeTree::scheduleDataProcessingJob(BackgroundJobsAssigne
     /// Depending on entry type execute in fetches (small) pool or big merge_mutate pool
     if (selected_entry->log_entry->type == LogEntry::GET_PART)
     {
-        executor.scheduleFetchTask(LambdaAdapter::create(
+        assignee.scheduleFetchTask(ExecutableLambdaAdapter::create(
             [this, selected_entry] () mutable
             {
                 return processQueueEntry(selected_entry);
@@ -3197,7 +3197,7 @@ bool StorageReplicatedMergeTree::scheduleDataProcessingJob(BackgroundJobsAssigne
     }
     else
     {
-        executor.scheduleMergeMutateTask(LambdaAdapter::create(
+        assignee.scheduleMergeMutateTask(ExecutableLambdaAdapter::create(
             [this, selected_entry] () mutable
             {
                 return processQueueEntry(selected_entry);
@@ -4337,7 +4337,7 @@ void StorageReplicatedMergeTree::shutdown()
     parts_mover.moves_blocker.cancelForever();
 
     restarting_thread.shutdown();
-    background_executor.finish();
+    background_operations_assignee.finish();
     part_moves_between_shards_orchestrator.shutdown();
 
     {
@@ -4347,7 +4347,7 @@ void StorageReplicatedMergeTree::shutdown()
         /// MUTATE, etc. query.
         queue.pull_log_blocker.cancelForever();
     }
-    background_moves_executor.finish();
+    background_moves_assignee.finish();
 
     auto data_parts_exchange_ptr = std::atomic_exchange(&data_parts_exchange_endpoint, InterserverIOEndpointPtr{});
     if (data_parts_exchange_ptr)
@@ -6947,9 +6947,9 @@ void StorageReplicatedMergeTree::onActionLockRemove(StorageActionBlockType actio
     if (action_type == ActionLocks::PartsMerge || action_type == ActionLocks::PartsTTLMerge
         || action_type == ActionLocks::PartsFetch || action_type == ActionLocks::PartsSend
         || action_type == ActionLocks::ReplicationQueue)
-        background_executor.trigger();
+        background_operations_assignee.trigger();
     else if (action_type == ActionLocks::PartsMove)
-        background_moves_executor.trigger();
+        background_moves_assignee.trigger();
 }
 
 bool StorageReplicatedMergeTree::waitForShrinkingQueueSize(size_t queue_size, UInt64 max_wait_milliseconds)
@@ -6961,7 +6961,7 @@ bool StorageReplicatedMergeTree::waitForShrinkingQueueSize(size_t queue_size, UI
 
     /// This is significant, because the execution of this task could be delayed at BackgroundPool.
     /// And we force it to be executed.
-    background_executor.trigger();
+    background_operations_assignee.trigger();
 
     Poco::Event target_size_event;
     auto callback = [&target_size_event, queue_size] (size_t new_queue_size)
@@ -7195,7 +7195,7 @@ MutationCommands StorageReplicatedMergeTree::getFirstAlterMutationCommandsForPar
 void StorageReplicatedMergeTree::startBackgroundMovesIfNeeded()
 {
     if (areBackgroundMovesNeeded())
-        background_moves_executor.start();
+        background_moves_assignee.start();
 }
 
 std::unique_ptr<MergeTreeSettings> StorageReplicatedMergeTree::getDefaultSettings() const

src/Storages/StorageReplicatedMergeTree.h

@@ -218,7 +218,7 @@ public:
                                               const zkutil::EphemeralNodeHolder::Ptr & metadata_drop_lock, Poco::Logger * logger);
 
     /// Schedules job to execute in background pool (merge, mutate, drop range and so on)
-    bool scheduleDataProcessingJob(BackgroundJobsAssignee & executor) override;
+    bool scheduleDataProcessingJob(BackgroundJobsAssignee & assignee) override;
 
     /// Checks that fetches are not disabled with action blocker and pool for fetches
     /// is not overloaded

tests/queries/0_stateless/01200_mutations_memory_consumption.reference

@@ -1,4 +1,4 @@
-1
-1
-1
-1
+[[1]]
+[[1]]
+[[1]]
+[[1]]

tests/queries/0_stateless/01200_mutations_memory_consumption.sql

@@ -6,7 +6,8 @@ CREATE TABLE table_with_single_pk
   value String
 )
 ENGINE = MergeTree
-ORDER BY key;
+ORDER BY key
+SETTINGS min_compress_block_size=65536, max_compress_block_size=65536;
 
 INSERT INTO table_with_single_pk SELECT number, toString(number % 10) FROM numbers(10000000);
 
@@ -15,9 +16,9 @@ ALTER TABLE table_with_single_pk DELETE WHERE key % 77 = 0 SETTINGS mutations_sy
 SYSTEM FLUSH LOGS;
 
 -- Memory usage for all mutations must be almost constant and less than
--- read_bytes (with a margin)
+-- read_bytes
 SELECT
-  DISTINCT 1.1 * read_bytes >= peak_memory_usage
+  arrayDistinct(groupArray(if (read_bytes >= peak_memory_usage, [1], [read_bytes, peak_memory_usage])))
 FROM
     system.part_log
 WHERE event_type = 'MutatePart' AND table = 'table_with_single_pk' AND database = currentDatabase();
@@ -34,7 +35,8 @@ CREATE TABLE table_with_multi_pk
   value String
 )
 ENGINE = MergeTree
-ORDER BY (key1, key2, key3);
+ORDER BY (key1, key2, key3)
+SETTINGS min_compress_block_size=65536, max_compress_block_size=65536;
 
 INSERT INTO table_with_multi_pk SELECT number % 32, number, toDateTime('2019-10-01 00:00:00'), toString(number % 10) FROM numbers(10000000);
 
@@ -43,9 +45,9 @@ ALTER TABLE table_with_multi_pk DELETE WHERE key1 % 77 = 0 SETTINGS mutations_sy
 SYSTEM FLUSH LOGS;
 
 -- Memory usage for all mutations must be almost constant and less than
--- read_bytes (with a margin)
+-- read_bytes
 SELECT
-  DISTINCT 1.1 * read_bytes >= peak_memory_usage
+  arrayDistinct(groupArray(if (read_bytes >= peak_memory_usage, [1], [read_bytes, peak_memory_usage])))
   FROM
       system.part_log
  WHERE event_type = 'MutatePart' AND table = 'table_with_multi_pk' AND database = currentDatabase();
@@ -64,7 +66,8 @@ CREATE TABLE table_with_function_pk
     value String
   )
 ENGINE = MergeTree
-ORDER BY (cast(value as UInt64), key2);
+ORDER BY (cast(value as UInt64), key2)
+SETTINGS min_compress_block_size=65536, max_compress_block_size=65536;
 
 INSERT INTO table_with_function_pk SELECT number % 32, number, toDateTime('2019-10-01 00:00:00'), toString(number % 10) FROM numbers(10000000);
 
@@ -73,9 +76,9 @@ ALTER TABLE table_with_function_pk DELETE WHERE key1 % 77 = 0 SETTINGS mutations
 SYSTEM FLUSH LOGS;
 
 -- Memory usage for all mutations must be almost constant and less than
--- read_bytes (with a margin)
+-- read_bytes
 SELECT
-  DISTINCT 1.1 * read_bytes >= peak_memory_usage
+  arrayDistinct(groupArray(if (read_bytes >= peak_memory_usage, [1], [read_bytes, peak_memory_usage])))
   FROM
       system.part_log
  WHERE event_type = 'MutatePart' AND table = 'table_with_function_pk' AND database = currentDatabase();
@@ -92,7 +95,8 @@ CREATE TABLE table_without_pk
   value String
 )
 ENGINE = MergeTree
-ORDER BY tuple();
+ORDER BY tuple()
+SETTINGS min_compress_block_size=65536, max_compress_block_size=65536;
 
 INSERT INTO table_without_pk SELECT number % 32, number, toDateTime('2019-10-01 00:00:00'), toString(number % 10) FROM numbers(10000000);
 
@@ -101,9 +105,9 @@ ALTER TABLE table_without_pk DELETE WHERE key1 % 77 = 0 SETTINGS mutations_sync
 SYSTEM FLUSH LOGS;
 
 -- Memory usage for all mutations must be almost constant and less than
--- read_bytes (with a margin)
+-- read_bytes
 SELECT
-  DISTINCT 1.1 * read_bytes >= peak_memory_usage
+  arrayDistinct(groupArray(if (read_bytes >= peak_memory_usage, [1], [read_bytes, peak_memory_usage])))
   FROM
       system.part_log
  WHERE event_type = 'MutatePart' AND table = 'table_without_pk' AND database = currentDatabase();