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602 lines
24 KiB
C++
602 lines
24 KiB
C++
#include <Storages/MergeTree/MergeTreePrefetchedReadPool.h>
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#include <Storages/MergeTree/MergeTreeBlockReadUtils.h>
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#include <Storages/MergeTree/MergeTreeBaseSelectProcessor.h>
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#include <Storages/MergeTree/RangesInDataPart.h>
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#include <Storages/MergeTree/MarkRange.h>
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#include <Storages/MergeTree/LoadedMergeTreeDataPartInfoForReader.h>
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#include <Storages/MergeTree/IMergeTreeReader.h>
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#include <Interpreters/threadPoolCallbackRunner.h>
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#include <Common/ElapsedTimeProfileEventIncrement.h>
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#include <IO/Operators.h>
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#include <base/getThreadId.h>
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namespace ProfileEvents
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{
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extern const Event MergeTreePrefetchedReadPoolInit;
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}
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namespace DB
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{
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namespace ErrorCodes
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{
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extern const int LOGICAL_ERROR;
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}
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MergeTreePrefetchedReadPool::MergeTreePrefetchedReadPool(
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size_t threads,
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size_t sum_marks_,
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size_t min_marks_for_concurrent_read_,
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RangesInDataParts && parts_,
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const StorageSnapshotPtr & storage_snapshot_,
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const PrewhereInfoPtr & prewhere_info_,
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const ExpressionActionsSettings & actions_settings_,
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const Names & column_names_,
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const Names & virtual_column_names_,
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size_t preferred_block_size_bytes_,
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const MergeTreeReaderSettings & reader_settings_,
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ContextPtr context_,
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bool use_uncompressed_cache_,
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bool is_remote_read_,
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const MergeTreeSettings & storage_settings_)
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: IMergeTreeReadPool(
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storage_snapshot_,
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column_names_,
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virtual_column_names_,
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min_marks_for_concurrent_read_,
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prewhere_info_,
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actions_settings_,
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reader_settings_,
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parts_,
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(preferred_block_size_bytes_ > 0),
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/*do_not_steal_tasks_*/false)
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, WithContext(context_)
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, log(&Poco::Logger::get("MergeTreePrefetchedReadPool(" + (parts_.empty() ? "" : parts_.front().data_part->storage.getStorageID().getNameForLogs()) + ")"))
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, header(storage_snapshot_->getSampleBlockForColumns(column_names_))
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, mark_cache(context_->getGlobalContext()->getMarkCache().get())
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, uncompressed_cache(use_uncompressed_cache_ ? context_->getGlobalContext()->getUncompressedCache().get() : nullptr)
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, profile_callback([this](ReadBufferFromFileBase::ProfileInfo info_) { profileFeedback(info_); })
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, index_granularity_bytes(storage_settings_.index_granularity_bytes)
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, fixed_index_granularity(storage_settings_.index_granularity)
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, is_remote_read(is_remote_read_)
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, prefetch_threadpool(getContext()->getPrefetchThreadpool())
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{
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/// Tasks creation might also create a lost of readers - check they do not
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/// do any time consuming operations in ctor.
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ProfileEventTimeIncrement<Milliseconds> watch(ProfileEvents::MergeTreePrefetchedReadPoolInit);
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parts_infos = getPartsInfos(parts_, preferred_block_size_bytes_);
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threads_tasks = createThreadsTasks(threads, sum_marks_, min_marks_for_concurrent_read_);
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}
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struct MergeTreePrefetchedReadPool::PartInfo
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{
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MergeTreeData::DataPartPtr data_part;
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size_t part_index_in_query;
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size_t sum_marks = 0;
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MarkRanges ranges;
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NameSet column_name_set;
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MergeTreeReadTaskColumns task_columns;
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MergeTreeBlockSizePredictorPtr size_predictor;
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size_t approx_size_of_mark = 0;
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size_t prefetch_step_marks = 0;
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};
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std::future<MergeTreeReaderPtr> MergeTreePrefetchedReadPool::createPrefetchedReader(
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const IMergeTreeDataPart & data_part,
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const NamesAndTypesList & columns,
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const MarkRanges & required_ranges,
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int64_t priority) const
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{
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auto reader = data_part.getReader(
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columns, storage_snapshot->metadata, required_ranges,
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uncompressed_cache, mark_cache, reader_settings,
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IMergeTreeReader::ValueSizeMap{}, profile_callback);
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/// In order to make a prefetch we need to wait for marks to be loaded. But we just created
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/// a reader (which starts loading marks in its constructor), then if we do prefetch right
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/// after creating a reader, it will be very inefficient. We can do prefetch for all parts
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/// only inside this MergeTreePrefetchedReadPool, where read tasks are created and distributed,
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/// and we cannot block either, therefore make prefetch inside the pool and put the future
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/// into the read task (MergeTreeReadTask). When a thread calls getTask(), it will wait for
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/// it (if not yet ready) after getting the task.
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auto task = [=, reader = std::move(reader), context = getContext()]() mutable -> MergeTreeReaderPtr &&
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{
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/// For async read metrics in system.query_log.
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PrefetchIncrement watch(context->getAsyncReadCounters());
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reader->prefetchBeginOfRange(priority);
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return std::move(reader);
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};
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return scheduleFromThreadPool<IMergeTreeDataPart::MergeTreeReaderPtr>(std::move(task), prefetch_threadpool, "ReadPrepare", priority);
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}
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void MergeTreePrefetchedReadPool::createPrefetchedReaderForTask(MergeTreeReadTask & task) const
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{
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if (task.reader.valid())
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throw Exception(ErrorCodes::LOGICAL_ERROR, "Task already has a reader");
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task.reader = createPrefetchedReader(*task.data_part, task.task_columns.columns, task.mark_ranges, task.priority);
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if (reader_settings.apply_deleted_mask && task.data_part->hasLightweightDelete())
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{
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auto pre_reader = createPrefetchedReader(*task.data_part, {LightweightDeleteDescription::FILTER_COLUMN}, task.mark_ranges, task.priority);
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task.pre_reader_for_step.push_back(std::move(pre_reader));
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}
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if (prewhere_info)
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{
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for (const auto & pre_columns_per_step : task.task_columns.pre_columns)
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{
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auto pre_reader = createPrefetchedReader(*task.data_part, pre_columns_per_step, task.mark_ranges, task.priority);
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task.pre_reader_for_step.push_back(std::move(pre_reader));
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}
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}
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}
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bool MergeTreePrefetchedReadPool::TaskHolder::operator <(const TaskHolder & other) const
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{
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return task->priority < other.task->priority;
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}
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void MergeTreePrefetchedReadPool::startPrefetches() const
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{
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for (const auto & task : prefetch_queue)
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{
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createPrefetchedReaderForTask(*task.task);
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}
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}
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MergeTreeReadTaskPtr MergeTreePrefetchedReadPool::getTask(size_t thread)
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{
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std::lock_guard lock(mutex);
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if (threads_tasks.empty())
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return nullptr;
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if (!started_prefetches)
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{
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startPrefetches();
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started_prefetches = true;
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}
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auto it = threads_tasks.find(thread);
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if (it == threads_tasks.end())
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{
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ThreadsTasks::iterator non_prefetched_tasks_to_steal = threads_tasks.end();
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ThreadsTasks::iterator prefetched_tasks_to_steal = threads_tasks.end();
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int64_t best_prefetched_task_priority = -1;
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/// There is no point stealing in order (like in MergeTreeReadPool, where tasks can be stolen
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/// only from the next thread). Even if we steal task from the next thread, which reads from
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/// the same part as we just read, it might seem that we can reuse our own reader, do some
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/// seek avoiding and it will have a good result as we avoided seek (new request). But it is
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/// not so, because this next task will most likely have its own reader a prefetch already on
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/// the fly. (Not to mention that in fact we cannot reuse our own reader if initially we did
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/// not accounted this range into range request to object storage).
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for (auto thread_tasks_it = threads_tasks.begin(); thread_tasks_it != threads_tasks.end(); ++thread_tasks_it)
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{
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/// Prefer to steal tasks which have an initialized reader (with prefetched data). Thus we avoid
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/// losing a prefetch by creating our own reader (or resusing our own reader if the part
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/// is the same as last read by this thread).
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auto & thread_tasks = thread_tasks_it->second;
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auto task_it = std::find_if(
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thread_tasks.begin(), thread_tasks.end(),
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[](const auto & task) { return task->reader.valid(); });
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if (task_it == thread_tasks.end())
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{
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/// The follow back to non-prefetched task should lie on the thread which
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/// has more tasks than others.
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if (non_prefetched_tasks_to_steal == threads_tasks.end()
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|| non_prefetched_tasks_to_steal->second.size() < thread_tasks.size())
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non_prefetched_tasks_to_steal = thread_tasks_it;
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}
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/// Try to steal task with the best (lowest) priority (because it will be executed faster).
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else if (prefetched_tasks_to_steal == threads_tasks.end()
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|| (*task_it)->priority < best_prefetched_task_priority)
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{
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best_prefetched_task_priority = (*task_it)->priority;
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chassert(best_prefetched_task_priority >= 0);
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prefetched_tasks_to_steal = thread_tasks_it;
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}
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}
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if (prefetched_tasks_to_steal != threads_tasks.end())
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{
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auto & thread_tasks = prefetched_tasks_to_steal->second;
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assert(!thread_tasks.empty());
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auto task_it = std::find_if(
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thread_tasks.begin(), thread_tasks.end(),
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[](const auto & task) { return task->reader.valid(); });
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assert(task_it != thread_tasks.end());
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auto task = std::move(*task_it);
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thread_tasks.erase(task_it);
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if (thread_tasks.empty())
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threads_tasks.erase(prefetched_tasks_to_steal);
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return task;
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}
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/// TODO: it also makes sense to first try to steal from the next thread if it has ranges
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/// from the same part as current thread last read - to reuse the reader.
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if (non_prefetched_tasks_to_steal != threads_tasks.end())
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{
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auto & thread_tasks = non_prefetched_tasks_to_steal->second;
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assert(!thread_tasks.empty());
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/// Get second half of the tasks.
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const size_t total_tasks = thread_tasks.size();
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const size_t half = total_tasks / 2;
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auto half_it = thread_tasks.begin() + half;
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assert(half_it != thread_tasks.end());
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/// Give them to current thread, as current thread's tasks list is empty.
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auto & current_thread_tasks = threads_tasks[thread];
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current_thread_tasks.insert(
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current_thread_tasks.end(), make_move_iterator(half_it), make_move_iterator(thread_tasks.end()));
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/// Erase them from the thread from which we steal.
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thread_tasks.resize(half);
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if (thread_tasks.empty())
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threads_tasks.erase(non_prefetched_tasks_to_steal);
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auto task = std::move(current_thread_tasks.front());
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current_thread_tasks.erase(current_thread_tasks.begin());
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if (current_thread_tasks.empty())
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threads_tasks.erase(thread);
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return task;
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}
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return nullptr;
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}
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auto & thread_tasks = it->second;
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assert(!thread_tasks.empty());
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auto task = std::move(thread_tasks.front());
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thread_tasks.pop_front();
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if (thread_tasks.empty())
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threads_tasks.erase(it);
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return task;
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}
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size_t MergeTreePrefetchedReadPool::getApproxSizeOfGranule(const IMergeTreeDataPart & part) const
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{
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const auto & columns = part.getColumns();
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auto all_columns_are_fixed_size = columns.end() == std::find_if(
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columns.begin(), columns.end(),
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[](const auto & col){ return col.type->haveMaximumSizeOfValue() == false; });
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if (all_columns_are_fixed_size)
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{
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size_t approx_size = 0;
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for (const auto & col : columns)
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approx_size += col.type->getMaximumSizeOfValueInMemory() * fixed_index_granularity;
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if (!index_granularity_bytes)
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return approx_size;
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return std::min(index_granularity_bytes, approx_size);
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}
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const size_t approx_size = static_cast<size_t>(std::round(static_cast<double>(part.getBytesOnDisk()) / part.getMarksCount()));
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if (!index_granularity_bytes)
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return approx_size;
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return std::min(index_granularity_bytes, approx_size);
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}
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MergeTreePrefetchedReadPool::PartsInfos MergeTreePrefetchedReadPool::getPartsInfos(
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const RangesInDataParts & parts, size_t preferred_block_size_bytes) const
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{
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PartsInfos result;
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Block sample_block = storage_snapshot->metadata->getSampleBlock();
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const bool predict_block_size_bytes = preferred_block_size_bytes > 0;
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for (const auto & part : parts)
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{
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auto part_info = std::make_unique<PartInfo>();
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part_info->data_part = part.data_part;
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part_info->part_index_in_query = part.part_index_in_query;
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part_info->ranges = part.ranges;
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std::sort(part_info->ranges.begin(), part_info->ranges.end());
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/// Sum up total size of all mark ranges in a data part.
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for (const auto & range : part.ranges)
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{
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part_info->sum_marks += range.end - range.begin;
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}
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part_info->approx_size_of_mark = getApproxSizeOfGranule(*part_info->data_part);
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const auto task_columns = getReadTaskColumns(
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LoadedMergeTreeDataPartInfoForReader(part.data_part),
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storage_snapshot,
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column_names,
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virtual_column_names,
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prewhere_info,
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actions_settings,
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reader_settings,
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/* with_subcolumns */true);
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part_info->size_predictor = !predict_block_size_bytes
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? nullptr
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: IMergeTreeSelectAlgorithm::getSizePredictor(part.data_part, task_columns, sample_block);
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/// Will be used to distinguish between PREWHERE and WHERE columns when applying filter.
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const auto & required_column_names = task_columns.columns.getNames();
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part_info->column_name_set = {required_column_names.begin(), required_column_names.end()};
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part_info->task_columns = task_columns;
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result.push_back(std::move(part_info));
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}
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return result;
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}
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MergeTreePrefetchedReadPool::ThreadsTasks MergeTreePrefetchedReadPool::createThreadsTasks(
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size_t threads, size_t sum_marks, size_t /* min_marks_for_concurrent_read */) const
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{
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if (parts_infos.empty())
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return {};
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const auto & context = getContext();
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const auto & settings = context->getSettingsRef();
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size_t total_size_approx = 0;
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for (const auto & part : parts_infos)
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{
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total_size_approx += part->sum_marks * part->approx_size_of_mark;
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}
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size_t min_prefetch_step_marks = 0;
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if (settings.filesystem_prefetches_limit && settings.filesystem_prefetches_limit < sum_marks)
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{
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min_prefetch_step_marks = static_cast<size_t>(std::round(static_cast<double>(sum_marks) / settings.filesystem_prefetches_limit));
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}
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size_t total_prefetches_approx = 0;
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for (const auto & part : parts_infos)
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{
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if (settings.filesystem_prefetch_step_marks)
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{
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part->prefetch_step_marks = settings.filesystem_prefetch_step_marks;
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}
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else if (settings.filesystem_prefetch_step_bytes && part->approx_size_of_mark)
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{
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part->prefetch_step_marks = std::max<size_t>(
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1, static_cast<size_t>(std::round(static_cast<double>(settings.filesystem_prefetch_step_bytes) / part->approx_size_of_mark)));
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}
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else
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{
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/// Experimentally derived ratio.
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part->prefetch_step_marks = static_cast<size_t>(
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std::round(std::pow(std::max<size_t>(1, static_cast<size_t>(std::round(sum_marks / 1000))), double(1.5))));
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}
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/// This limit is important to avoid spikes of slow aws getObject requests when parallelizing within one file.
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/// (The default is taken from here https://docs.aws.amazon.com/whitepapers/latest/s3-optimizing-performance-best-practices/use-byte-range-fetches.html).
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if (part->approx_size_of_mark
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&& settings.filesystem_prefetch_min_bytes_for_single_read_task
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&& part->approx_size_of_mark < settings.filesystem_prefetch_min_bytes_for_single_read_task)
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{
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const size_t new_min_prefetch_step_marks = static_cast<size_t>(
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std::ceil(static_cast<double>(settings.filesystem_prefetch_min_bytes_for_single_read_task) / part->approx_size_of_mark));
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if (min_prefetch_step_marks < new_min_prefetch_step_marks)
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{
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LOG_TEST(
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log, "Increasing min prefetch step from {} to {}", min_prefetch_step_marks, new_min_prefetch_step_marks);
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min_prefetch_step_marks = new_min_prefetch_step_marks;
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}
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}
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if (part->prefetch_step_marks < min_prefetch_step_marks)
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{
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LOG_TEST(
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log, "Increasing prefetch step from {} to {} because of the prefetches limit {}",
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part->prefetch_step_marks, min_prefetch_step_marks, settings.filesystem_prefetches_limit);
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part->prefetch_step_marks = min_prefetch_step_marks;
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}
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LOG_TEST(log,
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"Part: {}, sum_marks: {}, approx mark size: {}, prefetch_step_bytes: {}, prefetch_step_marks: {}, (ranges: {})",
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part->data_part->name, part->sum_marks, part->approx_size_of_mark,
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settings.filesystem_prefetch_step_bytes, part->prefetch_step_marks, toString(part->ranges));
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}
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const size_t min_marks_per_thread = (sum_marks - 1) / threads + 1;
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LOG_DEBUG(
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log,
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"Sum marks: {}, threads: {}, min_marks_per_thread: {}, result prefetch step marks: {}, prefetches limit: {}, total_size_approx: {}",
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sum_marks, threads, min_marks_per_thread, settings.filesystem_prefetch_step_bytes, settings.filesystem_prefetches_limit, total_size_approx);
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size_t current_prefetches_count = 0;
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prefetch_queue.reserve(total_prefetches_approx);
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ThreadsTasks result_threads_tasks;
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size_t memory_usage_approx = 0;
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for (size_t i = 0, part_idx = 0; i < threads && part_idx < parts_infos.size(); ++i)
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{
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auto need_marks = min_marks_per_thread;
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/// Priority is given according to the prefetch number for each thread,
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/// e.g. the first task of each thread has the same priority and is bigger
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/// than second task of each thread, and so on.
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/// Add 1 to query read priority because higher priority should be given to
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/// reads from pool which are from reader.
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int64_t priority = reader_settings.read_settings.priority + 1;
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while (need_marks > 0 && part_idx < parts_infos.size())
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{
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auto & part = *parts_infos[part_idx];
|
|
size_t & marks_in_part = part.sum_marks;
|
|
|
|
if (marks_in_part == 0)
|
|
{
|
|
++part_idx;
|
|
continue;
|
|
}
|
|
|
|
MarkRanges ranges_to_get_from_part;
|
|
size_t marks_to_get_from_part = std::min(need_marks, marks_in_part);
|
|
|
|
/// Split by prefetch step even if !allow_prefetch below. Because it will allow
|
|
/// to make a better distribution of tasks which did not fill into memory limit
|
|
/// or prefetches limit through tasks stealing.
|
|
if (part.prefetch_step_marks)
|
|
{
|
|
marks_to_get_from_part = std::min<size_t>(marks_to_get_from_part, part.prefetch_step_marks);
|
|
}
|
|
|
|
if (marks_in_part == marks_to_get_from_part)
|
|
{
|
|
ranges_to_get_from_part = part.ranges;
|
|
}
|
|
else
|
|
{
|
|
if (part.sum_marks < marks_to_get_from_part)
|
|
{
|
|
throw Exception(
|
|
ErrorCodes::LOGICAL_ERROR,
|
|
"Requested {} marks from part {}, but part has only {} marks",
|
|
marks_to_get_from_part, part.data_part->name, part.sum_marks);
|
|
}
|
|
|
|
size_t get_marks_num = marks_to_get_from_part;
|
|
while (get_marks_num > 0)
|
|
{
|
|
MarkRange & range = part.ranges.front();
|
|
const size_t marks_in_range = range.end - range.begin;
|
|
const size_t marks_to_get_from_range = std::min(marks_in_range, get_marks_num);
|
|
get_marks_num -= marks_to_get_from_range;
|
|
|
|
ranges_to_get_from_part.emplace_back(range.begin, range.begin + marks_to_get_from_range);
|
|
range.begin += marks_to_get_from_range;
|
|
|
|
if (range.begin == range.end)
|
|
{
|
|
part.ranges.pop_front();
|
|
}
|
|
else if (!get_marks_num && part.prefetch_step_marks && range.end - range.begin < part.prefetch_step_marks)
|
|
{
|
|
/// We already have `get_marks_num` marks, but current mark range has
|
|
/// less than `prefetch_step_marks` marks, then add them too.
|
|
ranges_to_get_from_part.emplace_back(range.begin, range.end);
|
|
marks_to_get_from_part += range.end - range.begin;
|
|
part.ranges.pop_front();
|
|
}
|
|
}
|
|
}
|
|
|
|
need_marks -= marks_to_get_from_part;
|
|
sum_marks -= marks_to_get_from_part;
|
|
marks_in_part -= marks_to_get_from_part;
|
|
|
|
auto curr_task_size_predictor = !part.size_predictor ? nullptr
|
|
: std::make_unique<MergeTreeBlockSizePredictor>(*part.size_predictor); /// make a copy
|
|
|
|
auto read_task = std::make_unique<MergeTreeReadTask>(
|
|
part.data_part, ranges_to_get_from_part, part.part_index_in_query,
|
|
part.column_name_set, part.task_columns, prewhere_info && prewhere_info->remove_prewhere_column,
|
|
std::move(curr_task_size_predictor));
|
|
|
|
read_task->priority = priority;
|
|
|
|
bool allow_prefetch = !settings.filesystem_prefetches_limit || current_prefetches_count + 1 <= settings.filesystem_prefetches_limit;
|
|
if (allow_prefetch && settings.filesystem_prefetch_max_memory_usage)
|
|
{
|
|
size_t num_readers = 1;
|
|
if (reader_settings.apply_deleted_mask && part.data_part->hasLightweightDelete())
|
|
++num_readers;
|
|
if (prewhere_info)
|
|
num_readers += part.task_columns.pre_columns.size();
|
|
memory_usage_approx += settings.max_read_buffer_size * num_readers;
|
|
|
|
allow_prefetch = memory_usage_approx <= settings.filesystem_prefetch_max_memory_usage;
|
|
}
|
|
if (allow_prefetch)
|
|
{
|
|
prefetch_queue.emplace(TaskHolder(read_task.get()));
|
|
++current_prefetches_count;
|
|
}
|
|
++priority;
|
|
|
|
result_threads_tasks[i].push_back(std::move(read_task));
|
|
}
|
|
}
|
|
|
|
LOG_TEST(
|
|
log, "Result tasks {} for {} threads: {}",
|
|
result_threads_tasks.size(), threads, dumpTasks(result_threads_tasks));
|
|
|
|
return result_threads_tasks;
|
|
}
|
|
|
|
MergeTreePrefetchedReadPool::~MergeTreePrefetchedReadPool()
|
|
{
|
|
for (const auto & [_, thread_tasks] : threads_tasks)
|
|
{
|
|
for (const auto & task : thread_tasks)
|
|
{
|
|
if (task->reader.valid())
|
|
task->reader.wait();
|
|
|
|
for (const auto & pre_reader : task->pre_reader_for_step)
|
|
{
|
|
if (pre_reader.valid())
|
|
pre_reader.wait();
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
std::string MergeTreePrefetchedReadPool::dumpTasks(const ThreadsTasks & tasks)
|
|
{
|
|
WriteBufferFromOwnString result;
|
|
for (const auto & [thread_id, thread_tasks] : tasks)
|
|
{
|
|
result << "\tthread id: " << toString(thread_id) << ", tasks: " << toString(thread_tasks.size());
|
|
if (!thread_tasks.empty())
|
|
{
|
|
size_t no = 0;
|
|
for (const auto & task : thread_tasks)
|
|
{
|
|
result << '\t';
|
|
result << ++no << ": ";
|
|
result << "reader: " << task->reader.valid() << ", ";
|
|
result << "part: " << task->data_part->name << ", ";
|
|
result << "ranges: " << toString(task->mark_ranges);
|
|
}
|
|
}
|
|
}
|
|
return result.str();
|
|
}
|
|
|
|
bool MergeTreePrefetchedReadPool::checkReadMethodAllowed(LocalFSReadMethod method)
|
|
{
|
|
return method == LocalFSReadMethod::pread_threadpool || method == LocalFSReadMethod::pread_fake_async;
|
|
}
|
|
bool MergeTreePrefetchedReadPool::checkReadMethodAllowed(RemoteFSReadMethod method)
|
|
{
|
|
return method == RemoteFSReadMethod::threadpool;
|
|
}
|
|
|
|
}
|