ClickHouse/src/Storages/MergeTree/MergeTreeBackgroundExecutor.cpp

#include <Storages/MergeTree/MergeTreeBackgroundExecutor.h>

#include <algorithm>

#include <Common/setThreadName.h>
#include <Storages/MergeTree/BackgroundJobsAssignee.h>


namespace DB
{


String MergeTreeBackgroundExecutor::toString(Type type)
{
    switch (type)
    {
        case Type::MERGE_MUTATE:
            return "MergeMutate";
        case Type::FETCH:
            return "Fetch";
        case Type::MOVE:
            return "Move";
    }
    __builtin_unreachable();
}


void MergeTreeBackgroundExecutor::updateConfiguration()
{
    auto new_threads_count = std::max<size_t>(1u, threads_count_getter());
    auto new_max_tasks_count = std::max<size_t>(1, max_task_count_getter());

    try
    {
        pending.set_capacity(new_max_tasks_count);
        active.set_capacity(new_max_tasks_count);

        pool.setMaxFreeThreads(0);
        pool.setMaxThreads(new_threads_count);
        pool.setQueueSize(new_max_tasks_count);

        /// 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); });
    }
    catch (...)
    {
        tryLogCurrentException(__PRETTY_FUNCTION__);
    }

    threads_count = new_threads_count;
    max_tasks_count = new_max_tasks_count;
}


void MergeTreeBackgroundExecutor::wait()
{
    {
        std::lock_guard lock(mutex);
        shutdown = true;
        has_tasks.notify_all();
    }

    pool.wait();
}


bool MergeTreeBackgroundExecutor::trySchedule(ExecutableTaskPtr task)
{
    std::lock_guard lock(mutex);

    if (shutdown)
        return false;

    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();
    }
    catch (...)
    {
        tryLogCurrentException(__PRETTY_FUNCTION__);
    }

    auto & value = CurrentMetrics::values[metric];
    if (value.load() >= static_cast<int64_t>(max_tasks_count))
        return false;

    pending.push_back(std::make_shared<TaskRuntimeData>(std::move(task), metric));

    has_tasks.notify_one();
    return true;
}


void MergeTreeBackgroundExecutor::removeTasksCorrespondingToStorage(StorageID id)
{
    std::vector<TaskRuntimeDataPtr> tasks_to_wait;
    {
        std::lock_guard lock(mutex);

        /// Erase storage related tasks from pending and select active tasks to wait for
        auto it = std::remove_if(pending.begin(), pending.end(),
            [&] (auto item) -> bool { return item->task->getStorageID() == id; });
        pending.erase(it, pending.end());

        /// Copy items to wait for their completion
        std::copy_if(active.begin(), active.end(), std::back_inserter(tasks_to_wait),
            [&] (auto item) -> bool { return item->task->getStorageID() == id; });

        for (auto & item : tasks_to_wait)
            item->is_currently_deleting = true;
    }


    for (auto & item : tasks_to_wait)
        item->is_done.wait();
}


void MergeTreeBackgroundExecutor::routine(TaskRuntimeDataPtr item)
{
    auto erase_from_active = [this, item]
    {
        active.erase(std::remove(active.begin(), active.end(), item), active.end());
    };

    try
    {
        if (item->task->executeStep())
        {
            std::lock_guard guard(mutex);

            if (item->is_currently_deleting)
            {
                erase_from_active();
                return;
            }

            pending.push_back(item);
            erase_from_active();
            has_tasks.notify_one();
            return;
        }

        {
            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.
        item->task->onCompleted();
        item->task.reset();
    }
    catch (...)
    {
        std::lock_guard guard(mutex);
        erase_from_active();
        has_tasks.notify_one();
        tryLogCurrentException(__PRETTY_FUNCTION__);
        /// Do not want any exceptions
        try { item->task->onCompleted(); } catch (...) {}
    }
}


void MergeTreeBackgroundExecutor::threadFunction(size_t number)
{
    setThreadName(name.c_str());

    while (true)
    {
        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;

            if (shutdown)
                break;

            item = std::move(pending.front());
            pending.pop_front();
            active.push_back(item);
        }

        routine(item);

        /// When storage shutdowns it will wait until all related background tasks
        /// are finished, because they may want to interact with its fields
        /// and this will cause segfault.
        if (item->is_currently_deleting)
            item->is_done.set();
    }
}


}