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40 lines
940 B
C++
40 lines
940 B
C++
#pragma once
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#include <IO/ReadBuffer.h>
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namespace DB
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{
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/** MMap range in a file and represent it as a ReadBuffer.
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* Please note that mmap is not always the optimal way to read file.
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* Also you cannot control whether and how long actual IO take place,
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* so this method is not manageable and not recommended for anything except benchmarks.
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*/
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class MMapReadBufferFromFileDescriptor : public ReadBuffer
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{
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protected:
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MMapReadBufferFromFileDescriptor() : ReadBuffer(nullptr, 0) {}
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void init(int fd_, size_t offset, size_t length_);
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void init(int fd_, size_t offset);
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public:
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MMapReadBufferFromFileDescriptor(int fd, size_t offset, size_t length);
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/// Map till end of file.
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MMapReadBufferFromFileDescriptor(int fd, size_t offset);
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~MMapReadBufferFromFileDescriptor() override;
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/// unmap memory before call to destructor
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void finish();
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private:
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size_t length = 0;
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int fd = -1;
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};
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}
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