ClickHouse/dbms/src/Storages/MergeTree/MergedColumnOnlyOutputStream.h

#pragma once

#include <Storages/MergeTree/IMergedBlockOutputStream.h>

namespace DB
{

class MergeTreeDataPartWriterWide;

/// Writes only those columns that are in `header`
class MergedColumnOnlyOutputStream final : public IMergedBlockOutputStream
{
public:
    /// skip_offsets: used when ALTERing columns if we know that array offsets are not altered.
    /// Pass empty 'already_written_offset_columns' first time then and pass the same object to subsequent instances of MergedColumnOnlyOutputStream
    ///  if you want to serialize elements of Nested data structure in different instances of MergedColumnOnlyOutputStream.
    MergedColumnOnlyOutputStream(
        const MergeTreeDataPartPtr & data_part, const Block & header_, bool sync_,
        CompressionCodecPtr default_codec_, bool skip_offsets_,
        const std::vector<MergeTreeIndexPtr> & indices_to_recalc_,
        WrittenOffsetColumns * offset_columns_ = nullptr,
        const MergeTreeIndexGranularity & index_granularity = {},
        const MergeTreeIndexGranularityInfo * index_granularity_info_ = nullptr,
        const String & filename_suffix = "");

    Block getHeader() const override { return header; }
    void write(const Block & block) override;
    void writeSuffix() override;
    MergeTreeData::DataPart::Checksums writeSuffixAndGetChecksums();

private:
    Block header;
    bool sync;
};


}