levelDB-LAB1-pzy_ckx/db/memtable.cc

// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#include "db/memtable.h"
#include "db/dbformat.h"
#include "leveldb/comparator.h"
#include "leveldb/env.h"
#include "leveldb/iterator.h"
#include "util/coding.h"
#include "include/leveldb/write_batch.h"

namespace leveldb {

static Slice GetLengthPrefixedSlice(const char* data) {
  uint32_t len;
  const char* p = data;
  p = GetVarint32Ptr(p, p + 5, &len);  // +5: we assume "p" is not corrupted
  return Slice(p, len);
}

MemTable::MemTable(const InternalKeyComparator& comparator)
    : comparator_(comparator), refs_(0), table_(comparator_, &arena_) {}

MemTable::~MemTable() { assert(refs_ == 0); }

size_t MemTable::ApproximateMemoryUsage() { return arena_.MemoryUsage(); }

int MemTable::KeyComparator::operator()(const char* aptr,
                                        const char* bptr) const {
  // Internal keys are encoded as length-prefixed strings.
  Slice a = GetLengthPrefixedSlice(aptr);
  Slice b = GetLengthPrefixedSlice(bptr);
  return comparator.Compare(a, b);
}

// Encode a suitable internal key target for "target" and return it.
// Uses *scratch as scratch space, and the returned pointer will point
// into this scratch space.
static const char* EncodeKey(std::string* scratch, const Slice& target) {
  scratch->clear();
  PutVarint32(scratch, target.size());
  scratch->append(target.data(), target.size());
  return scratch->data();
}

class MemTableIterator : public Iterator {
 public:
  explicit MemTableIterator(MemTable::Table* table) : iter_(table) {}

  MemTableIterator(const MemTableIterator&) = delete;
  MemTableIterator& operator=(const MemTableIterator&) = delete;

  ~MemTableIterator() override = default;

  bool Valid() const override { return iter_.Valid(); }
  void Seek(const Slice& k) override { iter_.Seek(EncodeKey(&tmp_, k)); }
  void SeekToFirst() override { iter_.SeekToFirst(); }
  void SeekToLast() override { iter_.SeekToLast(); }
  void Next() override { iter_.Next(); }
  void Prev() override { iter_.Prev(); }
  Slice key() const override { return GetLengthPrefixedSlice(iter_.key()); }
  Slice value() const override {
    Slice key_slice = GetLengthPrefixedSlice(iter_.key());
    return GetLengthPrefixedSlice(key_slice.data() + key_slice.size());
  }

  Status status() const override { return Status::OK(); }

 private:
  MemTable::Table::Iterator iter_;
  std::string tmp_;  // For passing to EncodeKey
};

Iterator* MemTable::NewIterator() { return new MemTableIterator(&table_); }

void MemTable::Add(SequenceNumber s, ValueType type, const Slice& key,
                   const Slice& value) {
  // Format of an entry is concatenation of:
  //  key_size     : varint32 of internal_key.size()
  //  key bytes    : char[internal_key.size()]
  //  tag          : uint64((sequence << 8) | type)
  //  value_size   : varint32 of value.size()
  //  value bytes  : char[value.size()]
  size_t key_size = key.size();
  size_t val_size = value.size();
  size_t internal_key_size = key_size + 8;
  const size_t encoded_len = VarintLength(internal_key_size) +
                             internal_key_size + VarintLength(val_size) +
                             val_size;
  char* buf = arena_.Allocate(encoded_len);
  char* p = EncodeVarint32(buf, internal_key_size);
  std::memcpy(p, key.data(), key_size);
  p += key_size;
  EncodeFixed64(p, (s << 8) | type);
  p += 8;
  p = EncodeVarint32(p, val_size);
  std::memcpy(p, value.data(), val_size);
  assert(p + val_size == buf + encoded_len);
  table_.Insert(buf);
}

bool MemTable::Get(const LookupKey& key, std::string* value, Status* s) { //燕改
    Slice memkey = key.memtable_key();
    Table::Iterator iter(&table_);
    iter.Seek(memkey.data());

    if (iter.Valid()) { // 获取跳表项的内容
      // entry format is:
      //    klength  varint32
      //    userkey  char[klength]
      //    tag      uint64
      //    vlength  varint32
      //    value    char[vlength]
      // Check that it belongs to same user key.  We do not check the
      // sequence number since the Seek() call above should have skipped
      // all entries with overly large sequence numbers.
        const char* entry = iter.key();
        uint32_t key_length;
        const char* key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);

        if (comparator_.comparator.user_comparator()->Compare(
                Slice(key_ptr, key_length - 8), key.user_key()) == 0) {
            const uint64_t tag = DecodeFixed64(key_ptr + key_length - 8);
            switch (static_cast<ValueType>(tag & 0xff)) {
                case kTypeValue: {
                    // 获取存储的值和时间戳
                    Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
                    std::string combined_str(v.data(), v.size());

                    // 根据存储格式分离原始值和时间戳
                    std::string actual_value = combined_str.substr(0, combined_str.size() - 20);
                    std::string time_str = combined_str.substr(combined_str.size() - 19, 19);

                    // 获取当前时间（字符串格式）
                    auto now = std::chrono::system_clock::now();
                    auto now_time_t = std::chrono::system_clock::to_time_t(now);
                    std::tm* now_tm = std::localtime(&now_time_t);
                    char buffer[20];
                    std::strftime(buffer, sizeof(buffer), "%Y-%m-%d %H:%M:%S", now_tm);
                    std::string current_time_str(buffer);

                    // 检查过期
                    if (time_str <= current_time_str) {
                        *s = Status::NotFound("Key has expired"); // 已过期
                        return true;
                    }

                    // 未过期，返回实际值
                    value->assign(actual_value);
                    return true;
                }
                case kTypeDeletion:
                    *s = Status::NotFound(Slice());
                    return true;
            }
        }
    }
    return false;
}



}  // namespace leveldb