​​​​​​RockDB 简单介绍

rocksDB 是一个可嵌入的，持久性的 key-value存储。

以下介绍来自rocksDB 中文官网 

https://rocksdb.org.cn/

它有以下四个特点

1 高性能：RocksDB使用一套日志结构的数据库引擎，为了更好的性能，这套引擎是用C++编写的。 Key和value是任意大小的字节流。

2 为快速存储而优化：RocksDB为快速而又低延迟的存储设备（例如闪存或者高速硬盘）而特殊优化处理。 RocksDB将最大限度的发挥闪存和RAM的高度率读写性能。

3 可适配性 ：RocksDB适合于多种不同工作量类型。 从像MyRocks这样的数据存储引擎， 到应用数据缓存, 甚至是一些嵌入式工作量，RocksDB都可以从容面对这些不同的数据工作量需求。

4 基础和高级的数据库操作  RocksDB提供了一些基础的操作，例如打开和关闭数据库。 对于合并和压缩过滤等高级操作，也提供了读写支持。

​​​​​​RockDB 安装与使用

rocksDB 安装有多种方式。由于官方没有提供对应平台的二进制库，所以需要自己编译使用。

rocksDB 的安装很简单，但是需要转变一下对于rocksDB 的看法。它不是一个重量级别的数据库，是一个嵌入式的key-value 存储。这意味着你只要在你的Maven项目中添加 rocksDB的依赖，就可以在开发环境中自我尝试了。如果你没有理解这点，你就可能会走入下面这两种不推荐的安装方式。

方式 1   去查看rocksDB 的官网 发现要写 一个C++ 程序（不推荐）

#include <assert> #include "rocksdb/db.h"  rocksdb::DB* db; rocksdb::Options options; options.create_if_missing = true; rocksdb::Status status =   rocksdb::DB::Open(options, "/tmp/testdb", &db); assert(status.ok());

创建一个数据库？？？？ 怎么和之前用的mysql 或者mongo 不一样，为啥没有一个start.sh 或者start.bat 之类的脚本。难道要我写。写完了编译发现还不知道怎么和rocksDB 库进行关联，怎么办，我C++都忘完了。

方式二  使用pyrocksDB （不推荐）

http://pyrocksdb.readthedocs.io/en/latest/installation.html

详细的安装文档见pyrocksDB 的官网安装文档。

以上两种方式对于熟悉C++ 或者python 的开发者来说都比较友好，但对于java 开发者来说不是太友好。

接下来就介绍第三种方式。

方式三 使用maven （推荐）

新建maven 项目，修改pom.xml 依赖里面添加

<dependency>     <groupId>org.rocksdb</groupId>     <artifactId>rocksdbjni</artifactId>     <version>5.8.6</version> </dependency>

可以选择你喜欢的版本。

然后更高maven 的语言级别，我这里全局设置为了1.8

<profiles>     <profile>         <id>jdk18</id>         <activation>             <activeByDefault>true</activeByDefault>             <jdk>1.8</jdk>         </activation>         <properties>             <maven.compiler.source>1.8</maven.compiler.source>             <maven.compiler.target>1.8</maven.compiler.target>             <maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>         </properties>     </profile> </profiles>

到这里，环境就装好了，是不是又回到了熟悉的java 世界。

然后copy 源码包下的一个类，在IDE中修改一下运行配置，加一个程序运行中数据库存储路径，就可以运行测试了 。我会在文章最后给出这个类。

运行控制台会有日志输出，同时也文件中也会出现一下新的文件。

后面会更新更多关于rockDB 开发API 的介绍，以及在生产中的应用，希望大家关注。

// Copyright (c) 2011-present, Facebook, Inc.  All rights reserved. //  This source code is licensed under both the GPLv2 (found in the //  COPYING file in the root directory) and Apache 2.0 License //  (found in the LICENSE.Apache file in the root directory).  import org.rocksdb.*; import org.rocksdb.util.SizeUnit;   import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.Map;  public class RocksDBSample {   static {     RocksDB.loadLibrary();   }    public static void main(final String[] args) {     if (args.length < 1) {       System.out.println("usage: RocksDBSample db_path");       System.exit(-1);     }      final String db_path = args[0];     final String db_path_not_found = db_path + "_not_found";      System.out.println("RocksDBSample");     try (final Options options = new Options();          final Filter bloomFilter = new BloomFilter(10);          final ReadOptions readOptions = new ReadOptions()              .setFillCache(false);          final Statistics stats = new Statistics();          final RateLimiter rateLimiter = new RateLimiter(10000000,10000, 10)) {        try (final RocksDB db = RocksDB.open(options, db_path_not_found)) {         assert (false);       } catch (final RocksDBException e) {         System.out.format("Caught the expected exception -- %s\n", e);       }        try {         options.setCreateIfMissing(true)             .setStatistics(stats)             .setWriteBufferSize(8 * SizeUnit.KB)             .setMaxWriteBufferNumber(3)             .setMaxBackgroundCompactions(10)             .setCompressionType(CompressionType.SNAPPY_COMPRESSION)             .setCompactionStyle(CompactionStyle.UNIVERSAL);       } catch (final IllegalArgumentException e) {         assert (false);       }        assert (options.createIfMissing() == true);       assert (options.writeBufferSize() == 8 * SizeUnit.KB);       assert (options.maxWriteBufferNumber() == 3);       assert (options.maxBackgroundCompactions() == 10);       assert (options.compressionType() == CompressionType.SNAPPY_COMPRESSION);       assert (options.compactionStyle() == CompactionStyle.UNIVERSAL);        assert (options.memTableFactoryName().equals("SkipListFactory"));       options.setMemTableConfig(           new HashSkipListMemTableConfig()               .setHeight(4)               .setBranchingFactor(4)               .setBucketCount(2000000));       assert (options.memTableFactoryName().equals("HashSkipListRepFactory"));        options.setMemTableConfig(           new HashLinkedListMemTableConfig()               .setBucketCount(100000));       assert (options.memTableFactoryName().equals("HashLinkedListRepFactory"));        options.setMemTableConfig(           new VectorMemTableConfig().setReservedSize(10000));       assert (options.memTableFactoryName().equals("VectorRepFactory"));        options.setMemTableConfig(new SkipListMemTableConfig());       assert (options.memTableFactoryName().equals("SkipListFactory"));        options.setTableFormatConfig(new PlainTableConfig());       // Plain-Table requires mmap read       options.setAllowMmapReads(true);       assert (options.tableFactoryName().equals("PlainTable"));        options.setRateLimiter(rateLimiter);        final BlockBasedTableConfig table_options = new BlockBasedTableConfig();       table_options.setBlockCacheSize(64 * SizeUnit.KB)           .setFilter(bloomFilter)           .setCacheNumShardBits(6)           .setBlockSizeDeviation(5)           .setBlockRestartInterval(10)           .setCacheIndexAndFilterBlocks(true)           .setHashIndexAllowCollision(false)           .setBlockCacheCompressedSize(64 * SizeUnit.KB)           .setBlockCacheCompressedNumShardBits(10);        assert (table_options.blockCacheSize() == 64 * SizeUnit.KB);       assert (table_options.cacheNumShardBits() == 6);       assert (table_options.blockSizeDeviation() == 5);       assert (table_options.blockRestartInterval() == 10);       assert (table_options.cacheIndexAndFilterBlocks() == true);       assert (table_options.hashIndexAllowCollision() == false);       assert (table_options.blockCacheCompressedSize() == 64 * SizeUnit.KB);       assert (table_options.blockCacheCompressedNumShardBits() == 10);        options.setTableFormatConfig(table_options);       assert (options.tableFactoryName().equals("BlockBasedTable"));        try (final RocksDB db = RocksDB.open(options, db_path)) {         db.put("hello".getBytes(), "world".getBytes());          final byte[] value = db.get("hello".getBytes());         assert ("world".equals(new String(value)));          final String str = db.getProperty("rocksdb.stats");         assert (str != null && !str.equals(""));       } catch (final RocksDBException e) {         System.out.format("[ERROR] caught the unexpected exception -- %s\n", e);         assert (false);       }        try (final RocksDB db = RocksDB.open(options, db_path)) {         db.put("hello".getBytes(), "world".getBytes());         byte[] value = db.get("hello".getBytes());         System.out.format("Get('hello') = %s\n",             new String(value));          for (int i = 1; i <= 9; ++i) {           for (int j = 1; j <= 9; ++j) {             db.put(String.format("%dx%d", i, j).getBytes(),                 String.format("%d", i * j).getBytes());           }         }          for (int i = 1; i <= 9; ++i) {           for (int j = 1; j <= 9; ++j) {             System.out.format("%s ", new String(db.get(                 String.format("%dx%d", i, j).getBytes())));           }           System.out.println("");         }          // write batch test         try (final WriteOptions writeOpt = new WriteOptions()) {           for (int i = 10; i <= 19; ++i) {             try (final WriteBatch batch = new WriteBatch()) {               for (int j = 10; j <= 19; ++j) {                 batch.put(String.format("%dx%d", i, j).getBytes(),                     String.format("%d", i * j).getBytes());               }               db.write(writeOpt, batch);             }           }         }         for (int i = 10; i <= 19; ++i) {           for (int j = 10; j <= 19; ++j) {             assert (new String(                 db.get(String.format("%dx%d", i, j).getBytes())).equals(                 String.format("%d", i * j)));             System.out.format("%s ", new String(db.get(                 String.format("%dx%d", i, j).getBytes())));           }           System.out.println("");         }          value = db.get("1x1".getBytes());         assert (value != null);         value = db.get("world".getBytes());         assert (value == null);         value = db.get(readOptions, "world".getBytes());         assert (value == null);          final byte[] testKey = "asdf".getBytes();         final byte[] testValue =             "asdfghjkl;'?><MNBVCXZQWERTYUIOP{+_)(*&^%$#@".getBytes();         db.put(testKey, testValue);         byte[] testResult = db.get(testKey);         assert (testResult != null);         assert (Arrays.equals(testValue, testResult));         assert (new String(testValue).equals(new String(testResult)));         testResult = db.get(readOptions, testKey);         assert (testResult != null);         assert (Arrays.equals(testValue, testResult));         assert (new String(testValue).equals(new String(testResult)));          final byte[] insufficientArray = new byte[10];         final byte[] enoughArray = new byte[50];         int len;         len = db.get(testKey, insufficientArray);         assert (len > insufficientArray.length);         len = db.get("asdfjkl;".getBytes(), enoughArray);         assert (len == RocksDB.NOT_FOUND);         len = db.get(testKey, enoughArray);         assert (len == testValue.length);          len = db.get(readOptions, testKey, insufficientArray);         assert (len > insufficientArray.length);         len = db.get(readOptions, "asdfjkl;".getBytes(), enoughArray);         assert (len == RocksDB.NOT_FOUND);         len = db.get(readOptions, testKey, enoughArray);         assert (len == testValue.length);          db.remove(testKey);         len = db.get(testKey, enoughArray);         assert (len == RocksDB.NOT_FOUND);          // repeat the test with WriteOptions         try (final WriteOptions writeOpts = new WriteOptions()) {           writeOpts.setSync(true);           writeOpts.setDisableWAL(true);           db.put(writeOpts, testKey, testValue);           len = db.get(testKey, enoughArray);           assert (len == testValue.length);           assert (new String(testValue).equals(               new String(enoughArray, 0, len)));         }          try {           for (final TickerType statsType : TickerType.values()) {             if (statsType != TickerType.TICKER_ENUM_MAX) {               stats.getTickerCount(statsType);             }           }           System.out.println("getTickerCount() passed.");         } catch (final Exception e) {           System.out.println("Failed in call to getTickerCount()");           assert (false); //Should never reach here.         }          try {           for (final HistogramType histogramType : HistogramType.values()) {             if (histogramType != HistogramType.HISTOGRAM_ENUM_MAX) {               HistogramData data = stats.getHistogramData(histogramType);             }           }           System.out.println("getHistogramData() passed.");         } catch (final Exception e) {           System.out.println("Failed in call to getHistogramData()");           assert (false); //Should never reach here.         }          try (final RocksIterator iterator = db.newIterator()) {            boolean seekToFirstPassed = false;           for (iterator.seekToFirst(); iterator.isValid(); iterator.next()) {             iterator.status();             assert (iterator.key() != null);             assert (iterator.value() != null);             seekToFirstPassed = true;           }           if (seekToFirstPassed) {             System.out.println("iterator seekToFirst tests passed.");           }            boolean seekToLastPassed = false;           for (iterator.seekToLast(); iterator.isValid(); iterator.prev()) {             iterator.status();             assert (iterator.key() != null);             assert (iterator.value() != null);             seekToLastPassed = true;           }            if (seekToLastPassed) {             System.out.println("iterator seekToLastPassed tests passed.");           }            iterator.seekToFirst();           iterator.seek(iterator.key());           assert (iterator.key() != null);           assert (iterator.value() != null);            System.out.println("iterator seek test passed.");          }         System.out.println("iterator tests passed.");          final List<byte[]> keys = new ArrayList<>();         try (final RocksIterator iterator = db.newIterator()) {           for (iterator.seekToLast(); iterator.isValid(); iterator.prev()) {             keys.add(iterator.key());           }         }          Map<byte[], byte[]> values = db.multiGet(keys);         assert (values.size() == keys.size());         for (final byte[] value1 : values.values()) {           assert (value1 != null);         }          values = db.multiGet(new ReadOptions(), keys);         assert (values.size() == keys.size());         for (final byte[] value1 : values.values()) {           assert (value1 != null);         }       } catch (final RocksDBException e) {         System.err.println(e);       }     }   } }