ClickHouse/src/Storages/MergeTree/MergeTreeReaderStream.cpp

#include <Storages/MergeTree/MergeTreeReaderStream.h>
#include <Compression/CachedCompressedReadBuffer.h>

#include <base/getThreadId.h>
#include <utility>


namespace DB
{

namespace ErrorCodes
{
    extern const int ARGUMENT_OUT_OF_BOUND;
    extern const int CANNOT_READ_ALL_DATA;
}

MergeTreeReaderStream::MergeTreeReaderStream(
        DiskPtr disk_,
        const String & path_prefix_, const String & data_file_extension_, size_t marks_count_,
        const MarkRanges & all_mark_ranges_,
        const MergeTreeReaderSettings & settings_,
        MarkCache * mark_cache_,
        UncompressedCache * uncompressed_cache_, size_t file_size_,
        const MergeTreeIndexGranularityInfo * index_granularity_info_,
        const ReadBufferFromFileBase::ProfileCallback & profile_callback_, clockid_t clock_type_,
        bool is_low_cardinality_dictionary_)
    : settings(settings_)
    , profile_callback(profile_callback_)
    , clock_type(clock_type_)
    , all_mark_ranges(all_mark_ranges_)
    , file_size(file_size_)
    , uncompressed_cache(uncompressed_cache_)
    , disk(std::move(disk_))
    , path_prefix(path_prefix_)
    , data_file_extension(data_file_extension_)
    , is_low_cardinality_dictionary(is_low_cardinality_dictionary_)
    , marks_count(marks_count_)
    , mark_cache(mark_cache_)
    , save_marks_in_cache(settings.save_marks_in_cache)
    , index_granularity_info(index_granularity_info_)
    , marks_loader(disk, mark_cache, index_granularity_info->getMarksFilePath(path_prefix),
        marks_count, *index_granularity_info, save_marks_in_cache) {}

void MergeTreeReaderStream::init()
{
    if (initialized)
        return;
    initialized = true;
    /// Compute the size of the buffer.
    size_t max_mark_range_bytes = 0;
    size_t sum_mark_range_bytes = 0;

    for (const auto & mark_range : all_mark_ranges)
    {
        size_t left_mark = mark_range.begin;
        size_t right_mark = mark_range.end;
        size_t left_offset = left_mark < marks_count ? marks_loader.getMark(left_mark).offset_in_compressed_file : 0;
        auto mark_range_bytes = getRightOffset(right_mark) - left_offset;

        max_mark_range_bytes = std::max(max_mark_range_bytes, mark_range_bytes);
        sum_mark_range_bytes += mark_range_bytes;
    }

    std::optional<size_t> estimated_sum_mark_range_bytes;
    if (sum_mark_range_bytes)
        estimated_sum_mark_range_bytes.emplace(sum_mark_range_bytes);

    /// Avoid empty buffer. May happen while reading dictionary for DataTypeLowCardinality.
    /// For example: part has single dictionary and all marks point to the same position.
    ReadSettings read_settings = settings.read_settings;
    if (max_mark_range_bytes != 0)
        read_settings = read_settings.adjustBufferSize(max_mark_range_bytes);

    //// Empty buffer does not makes progress.
    if (!read_settings.local_fs_buffer_size || !read_settings.remote_fs_buffer_size)
        throw Exception(ErrorCodes::CANNOT_READ_ALL_DATA, "Cannot read to empty buffer.");

    /// Initialize the objects that shall be used to perform read operations.
    if (uncompressed_cache)
    {
        auto buffer = std::make_unique<CachedCompressedReadBuffer>(
            fullPath(disk, path_prefix + data_file_extension),
            [this, estimated_sum_mark_range_bytes, read_settings]()
            {
                return disk->readFile(
                    path_prefix + data_file_extension,
                    read_settings,
                    estimated_sum_mark_range_bytes);
            },
            uncompressed_cache);

        if (profile_callback)
            buffer->setProfileCallback(profile_callback, clock_type);

        if (!settings.checksum_on_read)
            buffer->disableChecksumming();

        cached_buffer = std::move(buffer);
        data_buffer = cached_buffer.get();
        compressed_data_buffer = cached_buffer.get();
    }
    else
    {
        auto buffer = std::make_unique<CompressedReadBufferFromFile>(
            disk->readFile(
                path_prefix + data_file_extension,
                read_settings,
                estimated_sum_mark_range_bytes));

        if (profile_callback)
            buffer->setProfileCallback(profile_callback, clock_type);

        if (!settings.checksum_on_read)
            buffer->disableChecksumming();

        non_cached_buffer = std::move(buffer);
        data_buffer = non_cached_buffer.get();
        compressed_data_buffer = non_cached_buffer.get();
    }
}


size_t MergeTreeReaderStream::getRightOffset(size_t right_mark_non_included)
{
    /// NOTE: if we are reading the whole file, then right_mark == marks_count
    /// and we will use max_read_buffer_size for buffer size, thus avoiding the need to load marks.

    /// Special case, can happen in Collapsing/Replacing engines
    if (marks_count == 0)
        return 0;

    assert(right_mark_non_included <= marks_count);

    size_t result_right_offset;
    if (0 < right_mark_non_included && right_mark_non_included < marks_count)
    {
        auto right_mark = marks_loader.getMark(right_mark_non_included);
        result_right_offset = right_mark.offset_in_compressed_file;

        bool need_to_check_marks_from_the_right = false;

        /// If the end of range is inside the block, we will need to read it too.
        if (right_mark.offset_in_decompressed_block > 0)
        {
            need_to_check_marks_from_the_right = true;
        }
        else if (is_low_cardinality_dictionary)
        {
            /// Also, in LowCardinality dictionary several consecutive marks can point to
            /// the same offset. So to get true bytes offset we have to get first
            /// non-equal mark.
            /// Example:
            ///  Mark 186, points to [2003111, 0]
            ///  Mark 187, points to [2003111, 0]
            ///  Mark 188, points to [2003111, 0] <--- for example need to read until 188
            ///  Mark 189, points to [2003111, 0] <--- not suitable, because have same offset
            ///  Mark 190, points to [2003111, 0]
            ///  Mark 191, points to [2003111, 0]
            ///  Mark 192, points to [2081424, 0] <--- what we are looking for
            ///  Mark 193, points to [2081424, 0]
            ///  Mark 194, points to [2081424, 0]

            /// Also, in some cases, when one granule is not-atomically written (which is possible at merges)
            /// one granule may require reading of two dictionaries which starts from different marks.
            /// The only correct way is to take offset from at least next different granule from the right one.

            /// Check test_s3_low_cardinality_right_border.

            need_to_check_marks_from_the_right = true;
        }


        /// Let's go to the right and find mark with bigger offset in compressed file
        if (need_to_check_marks_from_the_right)
        {
            bool found_bigger_mark = false;
            for (size_t i = right_mark_non_included + 1; i < marks_count; ++i)
            {
                const auto & candidate_mark =  marks_loader.getMark(i);
                if (result_right_offset < candidate_mark.offset_in_compressed_file)
                {
                    result_right_offset = candidate_mark.offset_in_compressed_file;
                    found_bigger_mark = true;
                    break;
                }
            }

            if (!found_bigger_mark)
            {
                /// If there are no marks after the end of range, just use file size
                result_right_offset = file_size;
            }
        }
    }
    else if (right_mark_non_included == 0)
        result_right_offset = marks_loader.getMark(right_mark_non_included).offset_in_compressed_file;
    else
        result_right_offset = file_size;

    return result_right_offset;
}

void MergeTreeReaderStream::seekToMark(size_t index)
{
    init();
    MarkInCompressedFile mark = marks_loader.getMark(index);

    try
    {
        compressed_data_buffer->seek(mark.offset_in_compressed_file, mark.offset_in_decompressed_block);
    }
    catch (Exception & e)
    {
        /// Better diagnostics.
        if (e.code() == ErrorCodes::ARGUMENT_OUT_OF_BOUND)
            e.addMessage("(while seeking to mark " + toString(index)
                         + " of column " + path_prefix + "; offsets are: "
                         + toString(mark.offset_in_compressed_file) + " "
                         + toString(mark.offset_in_decompressed_block) + ")");

        throw;
    }
}


void MergeTreeReaderStream::seekToStart()
{
    init();
    try
    {
        compressed_data_buffer->seek(0, 0);
    }
    catch (Exception & e)
    {
        /// Better diagnostics.
        if (e.code() == ErrorCodes::ARGUMENT_OUT_OF_BOUND)
            e.addMessage("(while seeking to start of column " + path_prefix + ")");

        throw;
    }
}


void MergeTreeReaderStream::adjustRightMark(size_t right_mark)
{
    /**
     * Note: this method is called multiple times for the same range of marks -- each time we
     * read from stream, but we must update last_right_offset only if it is bigger than
     * the last one to avoid redundantly cancelling prefetches.
     */
    init();
    auto right_offset = getRightOffset(right_mark);
    if (!right_offset)
    {
        if (last_right_offset && *last_right_offset == 0)
            return;

        last_right_offset = 0; // Zero value means the end of file.
        data_buffer->setReadUntilEnd();
    }
    else
    {
        if (last_right_offset && right_offset <= last_right_offset.value())
            return;

        last_right_offset = right_offset;
        data_buffer->setReadUntilPosition(right_offset);
    }
}

ReadBuffer * MergeTreeReaderStream::getDataBuffer()
{
    init();
    return data_buffer;
}

CompressedReadBufferBase * MergeTreeReaderStream::getCompressedDataBuffer()
{
    init();
    return compressed_data_buffer;
}

}