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48 lines
1.2 KiB
C++
48 lines
1.2 KiB
C++
#pragma once
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#include <IO/ReadBufferFromFileBase.h>
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#include <IO/MMappedFileDescriptor.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 ReadBufferFromFileBase
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{
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public:
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off_t seek(off_t off, int whence) override;
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protected:
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MMapReadBufferFromFileDescriptor() = default;
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void init();
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MMappedFileDescriptor mapped;
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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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/// unmap memory before call to destructor
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void finish();
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off_t getPosition() override;
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std::string getFileName() const override;
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int getFD() const;
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size_t getFileSize() override;
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size_t readBigAt(char * to, size_t n, size_t offset, const std::function<bool(size_t)> &) const override;
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bool supportsReadAt() override { return true; }
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};
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}
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