ClickHouse/dbms/src/Storages/MergeTree/MergeTreeBaseBlockInputStream.cpp

#include "MergeTreeBaseBlockInputStream.h"
#include <Storages/MergeTree/MergeTreeReader.h>
#include <Storages/MergeTree/MergeTreeBlockReadUtils.h>
#include <Columns/ColumnConst.h>
#include <Columns/ColumnArray.h>
#include <Common/typeid_cast.h>
#include <ext/range.h>


namespace DB
{

namespace ErrorCodes
{
    extern const int ILLEGAL_TYPE_OF_COLUMN_FOR_FILTER;
    extern const int LOGICAL_ERROR;
}


MergeTreeBaseBlockInputStream::MergeTreeBaseBlockInputStream(
    MergeTreeData & storage,
    const ExpressionActionsPtr & prewhere_actions,
    const String & prewhere_column,
    size_t max_block_size_rows,
    size_t preferred_block_size_bytes,
    size_t preferred_max_column_in_block_size_bytes,
    size_t min_bytes_to_use_direct_io,
    size_t max_read_buffer_size,
    bool use_uncompressed_cache,
    bool save_marks_in_cache,
    const Names & virt_column_names)
:
    storage(storage),
    prewhere_actions(prewhere_actions),
    prewhere_column(prewhere_column),
    max_block_size_rows(max_block_size_rows),
    preferred_block_size_bytes(preferred_block_size_bytes),
    preferred_max_column_in_block_size_bytes(preferred_max_column_in_block_size_bytes),
    min_bytes_to_use_direct_io(min_bytes_to_use_direct_io),
    max_read_buffer_size(max_read_buffer_size),
    use_uncompressed_cache(use_uncompressed_cache),
    save_marks_in_cache(save_marks_in_cache),
    virt_column_names(virt_column_names),
    max_block_size_marks(max_block_size_rows / storage.index_granularity)
{
}


Block MergeTreeBaseBlockInputStream::readImpl()
{
    Block res;

    while (!res && !isCancelled())
    {
        if (!task && !getNewTask())
            break;

        res = readFromPart();

        if (res)
            injectVirtualColumns(res);

        if (task->isFinished())
            task.reset();
    }

    return res;
}


Block MergeTreeBaseBlockInputStream::readFromPart()
{
    Block res;

    if (task->size_predictor)
        task->size_predictor->startBlock();

    const auto max_block_size_rows = this->max_block_size_rows;
    const auto preferred_block_size_bytes = this->preferred_block_size_bytes;
    const auto preferred_max_column_in_block_size_bytes = this->preferred_max_column_in_block_size_bytes;
    const auto index_granularity = storage.index_granularity;
    const double min_filtration_ratio = 0.00001;

    auto estimateNumRows = [preferred_block_size_bytes, max_block_size_rows,
        index_granularity, preferred_max_column_in_block_size_bytes, min_filtration_ratio](
        MergeTreeReadTask & task, MergeTreeRangeReader & reader)
    {
        if (!task.size_predictor)
            return max_block_size_rows;

        /// Calculates number of rows will be read using preferred_block_size_bytes.
        /// Can't be less than index_granularity.
        size_t rows_to_read = task.size_predictor->estimateNumRows(preferred_block_size_bytes);
        if (!rows_to_read)
            return rows_to_read;
        rows_to_read = std::max(index_granularity, rows_to_read);

        if (preferred_max_column_in_block_size_bytes)
        {
            /// Calculates number of rows will be read using preferred_max_column_in_block_size_bytes.
            size_t rows_to_read_for_max_size_column
                = task.size_predictor->estimateNumRowsForMaxSizeColumn(preferred_max_column_in_block_size_bytes);
            double filtration_ratio = std::max(min_filtration_ratio, 1.0 - task.size_predictor->filtered_rows_ratio);
            size_t rows_to_read_for_max_size_column_with_filtration
                = static_cast<size_t>(rows_to_read_for_max_size_column / filtration_ratio);

            /// If preferred_max_column_in_block_size_bytes is used, number of rows to read can be less than index_granularity.
            rows_to_read = std::min(rows_to_read, rows_to_read_for_max_size_column_with_filtration);
        }

        size_t unread_rows_in_current_granule = reader.unreadRowsInCurrentGranule();
        if (unread_rows_in_current_granule >= rows_to_read)
            return rows_to_read;

        size_t granule_to_read = (rows_to_read + reader.readRowsInCurrentGranule() + index_granularity / 2) / index_granularity;
        return index_granularity * granule_to_read - reader.readRowsInCurrentGranule();
    };

    // read rows from reader and clear columns
    auto skipRows = [&estimateNumRows](
        Block & block, MergeTreeRangeReader & reader, MergeTreeReadTask & task, size_t rows)
    {
        size_t recommended_rows = rows;
        if (task.size_predictor)
            recommended_rows = std::max<size_t>(1, estimateNumRows(task, reader));
        while (rows)
        {
            size_t rows_to_skip = std::min(rows, recommended_rows);
            rows -= rows_to_skip;
            reader.read(block, rows_to_skip);
            for (const auto i : ext::range(0, block.columns()))
            {
                auto & col = block.getByPosition(i);
                if (task.column_name_set.count(col.name))
                {
                    if (ColumnArray * column_array = typeid_cast<ColumnArray *>(col.column.get()))
                    {
                        /// ColumnArray columns in block could have common offset column, which is used while reading.
                        /// This is in case of nested data structures.

                        /// Have to call resize(0) instead of cloneEmpty to save structure.
                        /// (To keep offsets possibly shared between different arrays.)
                        column_array->getOffsets().resize(0);
                        /// It's ok until multidimensional arrays are not stored in MergeTree.
                        column_array->getDataPtr() = column_array->getDataPtr()->cloneEmpty();
                    }
                    else
                        col.column = col.column->cloneEmpty();
                }
            }
        }
    };

    if (prewhere_actions)
    {
        do
        {
            /// Let's read the full block of columns needed to calculate the expression in PREWHERE.
            MarkRanges ranges_to_read;
            /// Last range may be partl read. The same number of rows we need to read after prewhere
            size_t rows_was_read_in_last_range = 0;
            std::optional<MergeTreeRangeReader> pre_range_reader;

            auto processNextRange = [& ranges_to_read, & rows_was_read_in_last_range, & pre_range_reader](
                MergeTreeReadTask & task, MergeTreeReader & pre_reader)
            {
                auto & range = task.mark_ranges.back();
                pre_range_reader = pre_reader.readRange(range.begin, range.end);
                ranges_to_read.push_back(range);
                rows_was_read_in_last_range = 0;
                task.mark_ranges.pop_back();
            };

            if (task->current_range_reader)
            {
                /// Havn't finihsed reading at last step. Copy state for prewhere columns
                pre_range_reader = task->current_range_reader->copyForReader(*pre_reader);
                if (task->number_of_rows_to_skip)
                {
                    /// number_of_rows_to_skip already was read for prewhere columns. skip them.
                    pre_range_reader = pre_range_reader->getFutureState(task->number_of_rows_to_skip);
                    pre_range_reader->disableNextSeek();
                }
            }
            else
                processNextRange(*task, *pre_reader);

            /// FIXME: size prediction model is updated by filtered rows, but it predicts size of unfiltered rows also
            size_t recommended_rows = estimateNumRows(*task, *pre_range_reader);
            if (res && recommended_rows < 1)
                break;
            size_t space_left = std::max(static_cast<decltype(max_block_size_rows)>(1), std::min(max_block_size_rows, recommended_rows));

            while ((pre_range_reader || !task->mark_ranges.empty()) && space_left && !isCancelled())
            {
                if (!pre_range_reader)
                    processNextRange(*task, *pre_reader);

                size_t rows_to_read = std::min(pre_range_reader->unreadRows(), space_left);
                size_t read_rows = pre_range_reader->read(res, rows_to_read);
                rows_was_read_in_last_range += read_rows;
                if (pre_range_reader->isReadingFinished())
                    pre_range_reader.reset();

                space_left -= read_rows;
            }

            /// In case of isCancelled.
            if (!res)
            {
                task->current_range_reader.reset();
                return res;
            }

            progressImpl({ res.rows(), res.bytes() });
            pre_reader->fillMissingColumns(res, task->ordered_names, task->should_reorder);

            /// Compute the expression in PREWHERE.
            prewhere_actions->execute(res);

            ColumnPtr column = res.getByName(prewhere_column).column;
            if (task->remove_prewhere_column)
                res.erase(prewhere_column);

            const auto pre_bytes = res.bytes();

            ColumnPtr observed_column;
            if (column->isNullable())
            {
                ColumnNullable & nullable_col = static_cast<ColumnNullable &>(*column);
                observed_column = nullable_col.getNestedColumn();
            }
            else
                observed_column = column;

            /** If the filter is a constant (for example, it says PREWHERE 1),
              * then either return an empty block, or return the block unchanged.
              */
            if (observed_column->isConst())
            {
                if (!static_cast<const ColumnConst &>(*observed_column).getValue<UInt8>())
                {
                    if (pre_range_reader)
                    {
                        /// Have to read rows from last partly read granula.
                        if (!ranges_to_read.empty())
                        {
                            auto & range = ranges_to_read.back();
                            task->current_range_reader = reader->readRange(range.begin, range.end);
                        }
                        /// But can just skip them.
                        task->number_of_rows_to_skip = rows_was_read_in_last_range;
                    }
                    else
                        task->current_range_reader.reset();

                    res.clear();
                    return res;
                }

                if (task->current_range_reader)
                {
                    if (task->number_of_rows_to_skip)
                        skipRows(res, *task->current_range_reader, *task, task->number_of_rows_to_skip);
                    size_t rows_to_read = ranges_to_read.empty()
                        ? rows_was_read_in_last_range : task->current_range_reader->unreadRows();
                    task->current_range_reader->read(res, rows_to_read);
                }

                for (auto range_idx : ext::range(0, ranges_to_read.size()))
                {
                    const auto & range = ranges_to_read[range_idx];
                    task->current_range_reader = reader->readRange(range.begin, range.end);
                    size_t rows_to_read = range_idx + 1 == ranges_to_read.size()
                        ? rows_was_read_in_last_range : task->current_range_reader->unreadRows();
                    task->current_range_reader->read(res, rows_to_read);
                }

                if (!pre_range_reader)
                    task->current_range_reader.reset();
                task->number_of_rows_to_skip = 0;

                progressImpl({ 0, res.bytes() - pre_bytes });
            }
            else if (const auto column_vec = typeid_cast<const ColumnUInt8 *>(observed_column.get()))
            {
                const auto & pre_filter = column_vec->getData();
                auto & number_of_rows_to_skip = task->number_of_rows_to_skip;
                if (!task->current_range_reader)
                    number_of_rows_to_skip = 0;
                IColumn::Filter post_filter(pre_filter.size());

                /// Let's read the rest of the columns in the required segments and compose our own filter for them.
                size_t pre_filter_pos = 0;
                size_t post_filter_pos = 0;

                size_t next_range_idx = 0;
                while (pre_filter_pos < pre_filter.size())
                {
                    if (!task->current_range_reader)
                    {
                        if (next_range_idx == ranges_to_read.size())
                            throw Exception("Not enough ranges to read after prewhere.", ErrorCodes::LOGICAL_ERROR);
                        const auto & range = ranges_to_read[next_range_idx++];
                        task->current_range_reader = reader->readRange(range.begin, range.end);
                    }
                    MergeTreeRangeReader & range_reader = *task->current_range_reader;
                    size_t current_range_rows_read = 0;
                    auto pre_filter_begin_pos = pre_filter_pos;

                    /// Now we need to read the same number of rows as in prewhere.
                    size_t rows_to_read = next_range_idx == ranges_to_read.size()
                        ? rows_was_read_in_last_range : (task->current_range_reader->unreadRows() - number_of_rows_to_skip);

                    auto readRows = [&]()
                    {
                        if (pre_filter_pos != pre_filter_begin_pos)
                        {
                            /// Fulfilling the promise to read (pre_filter_pos - pre_filter_begin_pos) rows
                            auto rows = pre_filter_pos - pre_filter_begin_pos;
                            memcpy(&post_filter[post_filter_pos], &pre_filter[pre_filter_begin_pos], rows);
                            post_filter_pos += rows;
                            current_range_rows_read += rows;
                            if (number_of_rows_to_skip)
                            {
                                /** Wasn't able to skip 'number_of_rows_to_skip' with false prewhere conditon
                                 * Just read them and throw away. */
                                skipRows(res, range_reader, *task, number_of_rows_to_skip);
                                number_of_rows_to_skip = 0;
                            }
                            range_reader.read(res, rows);
                        }
                    };

                    /** (pre_filter_pos - pre_filter_begin_pos) here is the number of rows we promies to read, but
                        haven't read yet to merge consecutive nonempy granulas. */
                    while (current_range_rows_read + (pre_filter_pos - pre_filter_begin_pos) < rows_to_read)
                    {
                        auto rows_should_be_copied = pre_filter_pos - pre_filter_begin_pos;
                        auto range_reader_with_skipped_rows = range_reader.getFutureState(number_of_rows_to_skip + rows_should_be_copied);
                        auto unread_rows_in_current_granule = range_reader_with_skipped_rows.unreadRowsInCurrentGranule();

                        const size_t limit = std::min(pre_filter.size(), pre_filter_pos + unread_rows_in_current_granule);
                        bool will_read_until_mark = unread_rows_in_current_granule == limit - pre_filter_pos;

                        UInt8 nonzero = 0;
                        for (size_t row = pre_filter_pos; row < limit; ++row)
                            nonzero |= pre_filter[row];

                        if (!nonzero)
                        {
                            /// Zero! Prewhere condition is false for all (limit - pre_filter_pos) rows.
                            readRows();

                            if (will_read_until_mark)
                            {
                                /// Can skip the rest of granule with false prewhere conditon right now.
                                do
                                {
                                    size_t rows_was_skipped = range_reader.skipToNextMark();
                                    if (number_of_rows_to_skip < rows_was_skipped)
                                    {
                                        current_range_rows_read += rows_was_skipped - number_of_rows_to_skip;
                                        number_of_rows_to_skip = 0;
                                    }
                                    else
                                        number_of_rows_to_skip -= rows_was_skipped;
                                }
                                while (number_of_rows_to_skip);
                            }
                            else
                            {
                                /// Here reading seems to be done. It's still possible to skip rows during next reading.
                                number_of_rows_to_skip += limit - pre_filter_pos;
                                current_range_rows_read += limit - pre_filter_pos;
                            }

                            pre_filter_begin_pos = limit;
                        }
                        pre_filter_pos = limit;
                    }

                    readRows();

                    if (next_range_idx != ranges_to_read.size())
                        task->current_range_reader.reset();
                }

                if (!pre_range_reader)
                    task->current_range_reader.reset();

                if (!post_filter_pos)
                {
                    if (task->size_predictor)
                        task->size_predictor->updateFilteredRowsRation(pre_filter.size(), pre_filter.size());
                    res.clear();
                    continue;
                }

                progressImpl({ 0, res.bytes() - pre_bytes });

                post_filter.resize(post_filter_pos);

                /// Filter the columns related to PREWHERE using pre_filter,
                ///  other columns - using post_filter.
                size_t rows = 0;
                for (const auto i : ext::range(0, res.columns()))
                {
                    auto & col = res.safeGetByPosition(i);
                    if (col.name == prewhere_column && res.columns() > 1)
                        continue;
                    col.column =
                        col.column->filter(task->column_name_set.count(col.name) ? post_filter : pre_filter, -1);
                    rows = col.column->size();
                }
                if (task->size_predictor)
                    task->size_predictor->updateFilteredRowsRation(pre_filter.size(), pre_filter.size() - rows);

                /// Replace column with condition value from PREWHERE to a constant.
                if (!task->remove_prewhere_column)
                    res.getByName(prewhere_column).column = DataTypeUInt8().createConstColumn(rows, UInt64(1));

            }
            else
                throw Exception{
                    "Illegal type " + column->getName() + " of column for filter. Must be ColumnUInt8 or ColumnConstUInt8.",
                    ErrorCodes::ILLEGAL_TYPE_OF_COLUMN_FOR_FILTER};

            if (res)
            {
                if (task->size_predictor)
                    task->size_predictor->update(res);

                reader->fillMissingColumnsAndReorder(res, task->ordered_names);
            }
        }
        while (!task->isFinished() && !res && !isCancelled());
    }
    else
    {
        size_t space_left = std::max(static_cast<decltype(max_block_size_rows)>(1), max_block_size_rows);
        while (!task->isFinished() && space_left && !isCancelled())
        {
            if (!task->current_range_reader)
            {
                auto & range = task->mark_ranges.back();
                task->current_range_reader = reader->readRange(range.begin, range.end);
                task->mark_ranges.pop_back();
            }

            size_t rows_to_read = space_left;
            size_t recommended_rows = estimateNumRows(*task, *task->current_range_reader);
            if (res && recommended_rows < 1)
                break;
            rows_to_read = std::min(rows_to_read, std::max(static_cast<decltype(recommended_rows)>(1), recommended_rows));

            size_t rows_was_read = task->current_range_reader->read(res, rows_to_read);
            if (task->current_range_reader->isReadingFinished())
                task->current_range_reader.reset();

            if (res && task->size_predictor)
            {
                task->size_predictor->update(res);
            }

            space_left -= rows_was_read;
        }

        /// In the case of isCancelled.
        if (!res)
            return res;

        progressImpl({ res.rows(), res.bytes() });
        reader->fillMissingColumns(res, task->ordered_names, task->should_reorder);
    }

    return res;
}


void MergeTreeBaseBlockInputStream::injectVirtualColumns(Block & block)
{
    const auto rows = block.rows();

    /// add virtual columns
    /// Except _sample_factor, which is added from the outside.
    if (!virt_column_names.empty())
    {
        for (const auto & virt_column_name : virt_column_names)
        {
            if (virt_column_name == "_part")
            {
                block.insert(ColumnWithTypeAndName{
                    DataTypeString().createConstColumn(rows, task->data_part->name)->convertToFullColumnIfConst(),
                    std::make_shared<DataTypeString>(),
                    virt_column_name});
            }
            else if (virt_column_name == "_part_index")
            {
                block.insert(ColumnWithTypeAndName{
                    DataTypeUInt64().createConstColumn(rows, static_cast<UInt64>(task->part_index_in_query))->convertToFullColumnIfConst(),
                    std::make_shared<DataTypeUInt64>(),
                    virt_column_name});
            }
        }
    }
}


MergeTreeBaseBlockInputStream::~MergeTreeBaseBlockInputStream() = default;

}