LevelDB源码阅读笔记（0、下载编译leveldb）
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LevelDB源码阅读笔记（0、下载编译leveldb）
本博客环境如下
[root@localhost build]# cat /etc/redhat-release
CentOS Linux release 7.9.2009 (Core)
简介
LevelDB是由Google使用C++开发的磁盘kv存储引擎。基于LSMTree使用顺序写（追加写）的方式实现了极高的写性能。RocksDB，Ceph等都可以看到它的身影。
环境搭建以及下载安装
命令如下：
# 下载
git clone https://github.com/google/leveldb.gitcd leveldbmkdir buildcd buildcmake ..
不出所料，会报错如下：
...CMake Error at CMakeLists.txt:303 (add_subdirectory):The source directory/root/workspace/leveldb/third_party/googletestdoes not contain a CMakeLists.txt file.CMake Error at CMakeLists.txt:307 (set_property):set_property could not find TARGET gtest. Perhaps it has not yet beencreated.CMake Error at CMakeLists.txt:309 (set_property):set_property could not find TARGET gmock. Perhaps it has not yet beencreated.CMake Error at CMakeLists.txt:411 (add_subdirectory):The source directory/root/workspace/leveldb/third_party/benchmarkdoes not contain a CMakeLists.txt file.-- Looking for sqlite3_open in sqlite3
-- Looking for sqlite3_open in sqlite3 - not found
...
此时需要进入项目的third_party目录下载三方依赖：
cd leveldb/third_partygit clone https://github.com/google/googletest.git
git clone https://github.com/google/benchmark.git
由于centos7.9下载的g++默认版本（默认是c++98）是：
[root@localhost build]# g++ --version
g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
直接make也会看到报错，这是因为leveldb要求至少是c++14，故需要升级g++：
yum install -y http://mirror.centos.org/centos/7/extras/x86_64/Packages/centos-release-scl-2-3.el7.centos.noarch.rpmyum install devtoolset-[g++版本号]-gcc-c++# 切换g++版本，仅对当前会话有效
# 也可以使用：source /opt/rh/devtoolset-[版本号]/enable
scl enable devtoolset-[g++版本号] bash
开始编译：
cd leveldb/buildcmake ..# 编译
make -j4## 在build目录下会生成一个静态库libleveldb.a
leveldb使用的小deamo，该测试文件位于leveldb项目的根目录：
// 文件名为：test.cc
#include <cassert>
#include <iostream>
#include <string>
#include "include/leveldb/db.h"int main() {leveldb::DB* db;leveldb::Options options;options.create_if_missing = true;leveldb::Status status = leveldb::DB::Open(options, "./data", &db);assert(status.ok());std::string key = "test_key";std::string write_value = "test_value";std::string read_value;leveldb::Status s = db->Put(leveldb::WriteOptions(), key, write_value);if (s.ok()){s = db->Get(leveldb::ReadOptions(), key, &read_value);}if (s.ok()){std::cout << "key=" << key << "\nvalue=" << read_value << std::endl;}else{std::cout << "failed to find the key!" << std::endl;}delete db;return 0;
}编译&运行：
// 使用如下命令也可以编译：
// g++ -I ./include -Wall -std=c++11 -o test.bin test.cc -L ./build/ -lpthread -lleveldb[root@localhost leveldb]# g++ -I ./include -Wall -std=c++11 -o test.bin test.cc ./build/libleveldb.a -lpthread
[root@localhost leveldb]# ./test.bin
key=test_key
value=test_value
本章完结
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