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58 lines
2.6 KiB
58 lines
2.6 KiB
#include <cstdint>
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#include "db/vlog_reader.h"
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#include "leveldb/slice.h"
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#include "leveldb/env.h"
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#include "util/coding.h"
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namespace leveldb{
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namespace vlog{
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VReader::VReader(SequentialFile* file) // A file abstraction for reading sequentially through a file
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:file_(file){}
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Status VReader::ReadRecord(uint64_t vfile_offset, std::string* record){
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Status s;
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Slice size_slice;
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char size_buf[11];
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uint64_t rec_size = 0;
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s = file_->SkipFromHead(vfile_offset); // 将文件的读取位置移动到 vfile_offset
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if(s.ok()) s = file_ -> Read(10, &size_slice, size_buf); // 先把Record 长度读出来, 最长10字节.
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if(s.ok()){
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if(GetVarint64(&size_slice, &rec_size) == false){ // 解析变长整数，得到记录的长度 rec_size
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return Status::Corruption("Failed to decode vlog record size.");
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}
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std::string rec;
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char* c_rec = new char[rec_size]; // 为记录分配一个临时缓冲区
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//TODO: Should delete c_rec?
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rec.resize(rec_size);
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Slice rec_slice;
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s = file_->SkipFromHead(vfile_offset + (size_slice.data() - size_buf)); // 将文件的读取位置移动
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if(!s.ok()) return s;
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s = file_-> Read(rec_size, &rec_slice, c_rec); // 从文件中读取 rec_size 字节的数据到 c_rec 中，并用 rec_slice 包装这些数据
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if(!s.ok()) return s;
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rec = std::string(c_rec, rec_size);
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*record = std::move(std::string(rec));
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}
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return s;
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}
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Status VReader::ReadKV(uint64_t vfile_offset, std::string* key, std::string* val){
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std::string record_str;
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Status s = ReadRecord(vfile_offset, &record_str);
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if(s.ok()){
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Slice record = Slice(record_str);
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//File the val
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uint64_t key_size;
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bool decode_flag = true;
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decode_flag &= GetVarint64(&record, &key_size); // 获取键的长度
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if(decode_flag){
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*key = Slice(record.data(), key_size).ToString(); // 从record中截取键值
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record = Slice(record.data() + key_size, record.size() - key_size); // 截取剩余的record
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}
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uint64_t val_size;
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decode_flag &= GetVarint64(&record, &val_size); // 获取value的长度
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if(decode_flag) *val = Slice(record.data(), val_size).ToString(); // 截取value的值
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if(!decode_flag || val->size() != record.size()){
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s = Status::Corruption("Failed to decode Record Read From vlog.");
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}
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}
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return s;
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}
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}// namespace vlog.
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}
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