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The Google LevelDB is a C/C++ key-value storage library, this means you can only write C/C++ code to use LevelDB. Unlike other key-value storage solution and MySQL, LevelDB doesn’t have a network server.

If you wan your PHP code to work with LevelDB, you can either wrap LevelDB as a PHP module, or wrap LevelDB as a network server. Writing a PHP LevelDB module is not a good idea most of the time, because we always want to connect to one LevelDB from several machines across network.

This is why I create SSDB – a LevelDB server with zset data type support. SSDB has a very simple network protocol, that can be implemented with many programming language, such as C, C++, PHP, Python, Cpy…

Here is a example of PHP operates with SSDB(LevelDB):

<?php
require_once('SSDB.php');
$ssdb = new SimpleSSDB('127.0.0.1', 8888);
$resp = $ssdb->set('key', '123');
$resp = $ssdb->get('key');
echo $resp; // output: 123

Download SSDB from: https://github.com/ideawu/ssdb

SSDB v1.1.0 is released! This version added the Online Backup feature, which allows to backup a SSDB instance without stopping service.

Quick Start

./tools/ssdb-dump 127.0.0.1 8888 backup_dir

A copy of SSDB instance(it is also the leveldb database) will be saved in a new created directory backup_dir.

Recover

Transfer the directory backup_dir to the server on which ssdb-server runs, then edit ssdb.conf to use backup_dir, restart ssdb-server.

Next Step

SSDB is now a productional storage server! The next feature that is planning to added is Replication(Master-Slave architecture). Replication is the base of distributed system.

SSDB Project: https://code.google.com/p/zdb/

SSDB version 1.0.1 is released. In this version, more commands are supported, these commands are:

keys, zkeys, hkeys, incr, decr, zincr, zdecr, hincr, hdecr

SSDB is used as cache server on www.udpwork.com, it works very well! So, don’t doubt to use SSDB for your project.

The Google leveldb is just a c++ library, cannot be directly used by PHP/Java/Python. As it is a library, data can’t be accessed across multi machines(not even multiprocesses in one machine).

SSDB(or zdb) is a network server that wrapping leveldb library, more important, besides key-value data type, SSDB supports zset(sorted set) and hash data type. Zset is the most valuable data type that widely used with Redis, to describe business abstracts such as inbox/outbox of a messaging system, posts list of a news site, etc.

SSDB’s client APIs currently including PHP, Python, Cpy, and more can be added easily.

Here is a list of SSDB features:

• Network wrapping of Google leveldb, client-server supports
• Persistent key-value, key-zset, key-hash storage
• Very fast(benchmark)

SSDB project: http://code.google.com/p/zdb/

The official levelDB does not support Cygwin platform, trying to compile it on Cygwin may get the error message:”Unknow platform”. Anyway, levelDB works on Windows Cygwin environment, all you have to do is to manually modify some files.

First, make sure your Cygwin has gcc-4 installed, not gcc-3:

$ gcc -v
gcc version 4.5.3 (GCC)

Then, edit build_detect_platform under levelDB source code folder, make it looks like this:

case "$TARGET_OS" in
    CYGWIN_*)
        PLATFORM=OS_LINUX
        COMMON_FLAGS="$MEMCMP_FLAG -lpthread -DOS_LINUX -DCYGWIN"
        PLATFORM_LDFLAGS="-lpthread"
        PORT_FILE=port/port_posix.cc
        ;;

The “CYGWIN_*” codes is added. Then edit port/port_posix.h, make it looks like this:

#if defined(OS_MACOSX) || defined(OS_SOLARIS) || defined(OS_FREEBSD) ||\
    defined(OS_NETBSD) || defined(OS_OPENBSD) || defined(OS_DRAGONFLYBSD) ||\
    defined(OS_ANDROID) || defined(OS_HPUX) || defined(CYGWIN)
// Use fread/fwrite/fflush on platforms without _unlocked variants
#define fread_unlocked fread
#define fwrite_unlocked fwrite
#define fflush_unlocked fflush
#endif

The ” || defined(CYGWIN)” is added, or you may got this error if you try to run make:

util/env_posix.cc:50: error: `fread_unlocked' undeclared (first use this function)

Now, you can compile levelDB on Windows Cygwin:

make

If you can find the file libleveldb.a in levelDB source code folder, it’s sucessfull. levelDB is just a library, not a standalone server, so we write a simple CPP code example to test it:

#include <iostream>
#include "leveldb/db.h"

int main(){
    leveldb::DB* db;
    leveldb::Options options;
    leveldb::Status status;

    options.create_if_missing = true;

    status = leveldb::DB::Open(options, "./testdb", &db);

    std::string key = "abc";
    std::string value = "123";
    std::string ret;
    std::cout << value;
    status = db->Put(leveldb::WriteOptions(), key, value);
    status = db->Get(leveldb::ReadOptions(), key, &ret);
    std::cout << ret;

    return 0;
}

Compile this code(file named a.cpp) and run with command:

g++ a.cpp -Iinclude -L. -lleveldb; ./a