1. Leveldb getting started

brief introduction

leveldb yes google A high performance of open source kv Data repository .

characteristic

• be based on LSM Mechanism to store data , High reading and writing performance ;
• key、value Support arbitrary byte Type array , Not just strings ;
• A persistent storage KV System , Store most of the data on disk ;
• according to key Values store data sequentially ;
• The operation interface is simple , The main interface is Put、Get、Delete;
• Support data snapshot The snapshot function , Read operations are not affected by write operations , Consistent data is always seen during read operations ;
• Support data compression (snappy Compress ) operation , Effectively reduce storage space 、 And increase speed IO efficiency ;

Use scenarios

• stand-alone kv Storage engine ;

Use samples

compile leveldb library

# git clone https://github.com/google/leveldb.git
# cd leveldb/
# git checkout -b 1.20 v1.20
//  compile 
# make
//  install 
# cp -rf include/leveldb/ /usr/include/
# cp out-shared/libleveldb.so* /usr/lib64/

Use samples

// test1.cpp
#include <cassert>
#include <iostream>
#include "leveldb/db.h"

int main() {
    leveldb::DB *db;
    leveldb::Options options;
    options.create_if_missing = true;
    leveldb::Status status = leveldb::DB::Open(options, "./test.db", &db);
    assert(status.ok());
    std::cout << "leveldb open success!" << std::endl;

    std::string key = "testkey1";
    std::string value = "testvalue1";
    db->Put(leveldb::WriteOptions(), key, value);
    std::cout << "put key " << key << " success" << std::endl;

    std::string value2;
    leveldb::Status s = db->Get(leveldb::ReadOptions(), key, &value2);
    if (s.ok()) {
        std::cout << "found key:" << key << ",value:" << value2 << std::endl;
    }
	
    s = db->Delete(leveldb::WriteOptions(), key);
    if (s.ok()) {
        std::cout << "delete key success which key:" << key << std::endl;
    }

    s = db->Get(leveldb::ReadOptions(), key, &value2);
    if (s.IsNotFound()) {
        std::cout << "can not found after delete for key:" << key << std::endl;
    }

    delete db;
    return 0;
}

compile

# g++ -lpthread -lleveldb -o test1 test1.cpp

function

# ./test1 
leveldb open success!
put key testkey1 success
found key:testkey1,value:testvalue1
delete key success which key:testkey1
can not found after delete for key:testkey1

Data files

# tree test.db/
test.db/
├── 000003.log
├── CURRENT
├── LOCK
├── LOG
└── MANIFEST-000002