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#pragma once
#include <IO/ReadBufferFromFileBase.h>
#include <IO/MMappedFileDescriptor.h>
namespace DB
{
/** MMap range in a file and represent it as a ReadBuffer.
* Please note that mmap is not always the optimal way to read file.
* Also you cannot control whether and how long actual IO take place,
* so this method is not manageable and not recommended for anything except benchmarks.
*/
class MMapReadBufferFromFileDescriptor : public ReadBufferFromFileBase
{
public:
off_t seek(off_t off, int whence) override;
protected:
MMapReadBufferFromFileDescriptor() = default;
void init();
MMappedFileDescriptor mapped;
public:
MMapReadBufferFromFileDescriptor(int fd_, size_t offset_, size_t length_);
/// Map till end of file.
MMapReadBufferFromFileDescriptor(int fd_, size_t offset_);
/// unmap memory before call to destructor
void finish();
off_t getPosition() override;
std::string getFileName() const override;
int getFD() const;
size_t getFileSize() override;
size_t readBigAt(char * to, size_t n, size_t offset, const std::function<bool(size_t)> &) override;
bool supportsReadAt() override { return true; }
};
}
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