Add函數(shù)是給一個(gè)Data block中添加對(duì)應(yīng)的key和value,函數(shù)源碼如下,其中有一處不理解:

L30~L34是更新last_key_的,不理解這里干嘛不直接last_key_ = key.ToString();

寫(xiě)成

// Update state
last_key_.resize(shared);
last_key_.append(key.data() + shared, non_shared);
assert(Slice(last_key_) == key);

是有什么其他原因嗎?

1 void BlockBuilder::Add(const Slice& key, const Slice& value) { 2 Slice last_key_piece(last_key_); 3 assert(!finished_); 4 assert(counter_ <= options_->block_restart_interval); 5 assert(buffer_.empty() // No values yet? 6 || options_->comparator->Compare(key, last_key_piece) > 0); 7 size_t shared = 0; 8 if (counter_ < options_->block_restart_interval) { 9 // See how much sharing to do with previous string 10 const size_t min_length = std::min(last_key_piece.size(), key.size()); 11 while ((shared < min_length) && (last_key_piece[shared] == key[shared])) { 12 shared++; 13 } 14 } else { 15 // Restart compression 16 restarts_.push_back(buffer_.size()); 17 counter_ = 0; 18 } 19 const size_t non_shared = key.size() - shared; 20 21 // Add "<shared><non_shared><value_size>" to buffer_ 22 PutVarint32(&buffer_, shared); 23 PutVarint32(&buffer_, non_shared); 24 PutVarint32(&buffer_, value.size()); 25 26 // Add string delta to buffer_ followed by value 27 buffer_.append(key.data() + shared, non_shared); 28 buffer_.append(value.data(), value.size()); 29 30 // Update state 31 last_key_.resize(shared); 32 last_key_.append(key.data() + shared, non_shared); 33 assert(Slice(last_key_) == key); 34 counter_++; 35 }

?

轉(zhuǎn)載于:https://www.cnblogs.com/i4oolish/p/4084007.html

總結(jié)

以上是生活随笔為你收集整理的[Leveldb源码剖析疑问]-block_builder.cc之Add函数的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問(wèn)題。

如果覺(jué)得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。