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

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

#include <utility>


namespace DB
{

namespace ErrorCodes
{
    extern const int ARGUMENT_OUT_OF_BOUND;
}


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)
        : disk(std::move(disk_)), path_prefix(path_prefix_), data_file_extension(data_file_extension_), 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)
{
    /// 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;

        /// 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.

        /// If the end of range is inside the block, we will need to read it too.
        if (right_mark < marks_count && marks_loader.getMark(right_mark).offset_in_decompressed_block > 0)
        {
            while (right_mark < marks_count
                && marks_loader.getMark(right_mark).offset_in_compressed_file == marks_loader.getMark(mark_range.end).offset_in_compressed_file)
            {
                ++right_mark;
            }
        }

        size_t mark_range_bytes;

        /// If there are no marks after the end of range, just use file size
        if (right_mark >= marks_count
            || (right_mark + 1 == marks_count
                && marks_loader.getMark(right_mark).offset_in_compressed_file == marks_loader.getMark(mark_range.end).offset_in_compressed_file))
        {
            mark_range_bytes = file_size - (left_mark < marks_count ? marks_loader.getMark(left_mark).offset_in_compressed_file : 0);
        }
        else
        {
            mark_range_bytes = marks_loader.getMark(right_mark).offset_in_compressed_file - marks_loader.getMark(left_mark).offset_in_compressed_file;
        }

        max_mark_range_bytes = std::max(max_mark_range_bytes, mark_range_bytes);
        sum_mark_range_bytes += 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.
    if (max_mark_range_bytes == 0)
        max_mark_range_bytes = settings.max_read_buffer_size;

    size_t buffer_size = std::min(settings.max_read_buffer_size, max_mark_range_bytes);

    /// 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, buffer_size, sum_mark_range_bytes, &settings]()
            {
                return disk->readFile(
                    path_prefix + data_file_extension,
                    buffer_size,
                    sum_mark_range_bytes,
                    settings.min_bytes_to_use_direct_io,
                    settings.min_bytes_to_use_mmap_io);
            },
            uncompressed_cache);

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

        cached_buffer = std::move(buffer);
        data_buffer = cached_buffer.get();
    }
    else
    {
        auto buffer = std::make_unique<CompressedReadBufferFromFile>(
            disk->readFile(path_prefix + data_file_extension, buffer_size,
                sum_mark_range_bytes, settings.min_bytes_to_use_direct_io, settings.min_bytes_to_use_mmap_io)
        );

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

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


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

    try
    {
        if (cached_buffer)
            cached_buffer->seek(mark.offset_in_compressed_file, mark.offset_in_decompressed_block);
        if (non_cached_buffer)
            non_cached_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()
{
    try
    {
        if (cached_buffer)
            cached_buffer->seek(0, 0);
        if (non_cached_buffer)
            non_cached_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;
    }
}

}