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#pragma once
#include <Compression/CompressedReadBufferBase.h>
#include <IO/ReadBufferFromFileBase.h>
#include <IO/ReadSettings.h>
#include <time.h>
#include <memory>
namespace DB
{
class MMappedFileCache;
/// Unlike CompressedReadBuffer, it can do seek.
class CompressedReadBufferFromFile final : public CompressedReadBufferBase, public BufferWithOwnMemory<ReadBuffer>
{
private:
/** At any time, one of two things is true:
* a) size_compressed = 0
* b)
* - `working_buffer` contains the entire block.
* - `file_in` points to the end of this block.
* - `size_compressed` contains the compressed size of this block.
*/
std::unique_ptr<ReadBufferFromFileBase> p_file_in;
ReadBufferFromFileBase & file_in;
size_t size_compressed = 0;
/// This field inherited from ReadBuffer. It's used to perform "lazy" seek, so in seek() call we:
/// 1) actually seek only underlying compressed file_in to offset_in_compressed_file;
/// 2) reset current working_buffer;
/// 3) remember the position in decompressed block in nextimpl_working_buffer_offset.
/// After following ReadBuffer::next() -> nextImpl call we will read new data into working_buffer and
/// ReadBuffer::next() will move our position in the fresh working_buffer to nextimpl_working_buffer_offset and
/// reset it to zero.
///
/// NOTE: We have independent readBig implementation, so we have to take
/// nextimpl_working_buffer_offset into account there as well.
///
/* size_t nextimpl_working_buffer_offset; */
bool nextImpl() override;
void prefetch(Priority priority) override;
public:
explicit CompressedReadBufferFromFile(std::unique_ptr<ReadBufferFromFileBase> buf, bool allow_different_codecs_ = false);
/// Seek is lazy in some sense. We move position in compressed file_in to offset_in_compressed_file, but don't
/// read data into working_buffer and don't shift our position to offset_in_decompressed_block. Instead
/// we store this offset inside nextimpl_working_buffer_offset.
void seek(size_t offset_in_compressed_file, size_t offset_in_decompressed_block) override;
[[nodiscard]] size_t readBig(char * to, size_t n) override;
void setProfileCallback(const ReadBufferFromFileBase::ProfileCallback & profile_callback_, clockid_t clock_type_ = CLOCK_MONOTONIC_COARSE)
{
file_in.setProfileCallback(profile_callback_, clock_type_);
}
void setReadUntilPosition(size_t position) override { file_in.setReadUntilPosition(position); }
void setReadUntilEnd() override { file_in.setReadUntilEnd(); }
};
}
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