Rocksdb基本用法

rocksdb 用法簡單介紹

1. RocksDB是使用C++編寫的嵌入式kv存儲引擎，其鍵值均允許使用二進制流。由Facebook基於levelDB開發， 提供向后兼容的levelDB API。
   RocksDB針對Flash存儲進行優化，延遲極小。RocksDB使用LSM存儲引擎，純C++編寫。

2. 打開一個數據庫
   rocksdb::DB* db;
   rocksdb::Options options;
   options.create_if_missing = true;
   rocksdb::Status status = rocksdb::DB::Open(options, "/tmp/testdb", &db);
   assert(status.ok());

3. 往數據庫寫入kv鍵值對
   s = db->Put(WriteOptions(), "k1", "v1");

4. 向數據庫查詢k的value
   s = db->Get(ReadOptions(), "k1", &v);

5. 原子寫入
   rocksdb::WriteBatch batch;
   batch.Delete("k1");
   batch.Put("k2", "v2");
   s = db->Write(rocksdb::WriteOptions(), &batch);

6. 迭代器
   db->NewIterator(rocksdb::ReadOptions());
   可以通過在調用NewIterator的時候，給傳入的option設定ReadOptions.iterate_upper_bound來為你的迭代范圍設置一個上邊界。
   通過這個設定，rocksdb就不用繼續查找這個key之后的內容了。在一些情況下，可以節省一些IO和計算。在特定的工作載荷下，
   它帶來的改善是顯著的。這個選項可以同在正向和反向迭代。

   rocksdb::Iterator* it = db->NewIterator(rocksdb::ReadOptions());
   for (it->SeekToFirst(); it->Valid(); it->Next()) {
   cout << it->key().ToString() << ": " << it->value().ToString() << endl;
   }

7. 事務操作
   Status s = TransactionDB::Open(options,txn_db_options,kDbPathTran,&txn_db );
   Transaction* txn = txn_db->BeginTransaction(WriteOptions());
   獲得事務，就可以進行相應的op操作，如下：
   s = txn->Put("key", "value");
   s = txn->Delete("key2");
   然后對事務進行提交
   s = txn->Commit();

rocksdb實際用法如以下代碼

#include<cstdio>
#include<string>
#include<iostream>
#include "rocksdb/db.h"
#include "rocksdb/slice.h"
#include "rocksdb/options.h"
#include "rocksdb/utilities/transaction.h"
#include "rocksdb/utilities/transaction_db.h"
using namespace rocksdb;

std::string kDbPath = "/tmp/wsf_rocksdb_test";
std::string kDbPathTran = "/tmp/wsf_rocksdb_transation";

void testTransaction(){
     TransactionDB* txn_db;
     Options options;        
     TransactionDBOptions txn_db_options;
     options.create_if_missing = true;


     Status s = TransactionDB::Open(options,txn_db_options,kDbPathTran,&txn_db );
     Transaction* txn = txn_db->BeginTransaction(WriteOptions());
     s = txn->Put("key", "value");
     s = txn->Delete("key2");
     s = txn->Merge("key3", "value");
     s = txn->Commit();
     delete txn;

}

int main()
{
    DB *db;
    Options options;
    options.create_if_missing = true;

    Status s = DB::Open(options, kDbPath, &db);
    assert(s.ok());

    s = db->Put(WriteOptions(), "k1", "v1");
    assert(s.ok());

    std::string v;
    s = db->Get(ReadOptions(), "k1", &v);
    assert(s.ok());
    std::cout << "v = " << v << std::endl;

    rocksdb::WriteBatch batch;
    batch.Delete("k1");
    batch.Put("k2", "v2");
    batch.Put("k3", "v3");
    batch.Put("k4", "v4");
    s = db->Write(rocksdb::WriteOptions(), &batch);
    if (s.ok()) {
	std::string v2;
	s = db->Get(ReadOptions(), "k2", &v2);
	std::cout << "v = " << v2 << std::endl;
	s = db->Get(ReadOptions(), "k1", &v);
	if (!s.ok()) {
	    std::cout << s.ToString() << std::endl;
	}
	// assert(s.ok());
	//std::cout<<"v = "<<v<<std::endl;
    }

    rocksdb::Iterator * it = db->NewIterator(rocksdb::ReadOptions());
    for (it->SeekToFirst(); it->Valid(); it->Next()) {
	std::cout << it->key().ToString() << ":" << it->value().
	    ToString() << std::endl;
    }

    testTransaction();
}