Apache Drill学习笔记一：环境搭建和简单试用

简介

Apache Drill是一个低延迟的分布式海量数据（涵盖结构化、半结构化以及嵌套数据）交互式查询引擎，使用ANSI SQL兼容语法，支持本地文件、HDFS、HBase、MongoDB等后端存储，支持Parquet、JSON、CSV、TSV、PSV等数据格式。受Google的Dremel启发，Drill知足上千节点的PB级别数据的交互式商业智能分析场景。

安装

Drill能够安装在单机或者集群环境上，支持Linux、Windows、Mac OS X系统。简单起见，咱们在Linux单机环境（CentOS 6.3）搭建以供试用。

准备安装包：

• jdk 7：jdk-7u75-linux-x64.tar.gz
• Drill：apache-drill-0.8.0.tar.gz

在$WORK（/path/to/work）目录中安装，将jdk和drill分别解压到java和drill目录中，并打软连以便升级：

.
├── drill
│   ├── apache-drill -> apache-drill-0.8.0
│   └── apache-drill-0.8.0
├── init.sh
└── java
    ├── jdk -> jdk1.7.0_75
    └── jdk1.7.0_75

并添加一init.sh脚本初始化java相关环境变量：

export WORK="/path/to/work"
export JAVA="$WORK/java/jdk/bin/java"
export JAVA_HOME="$WORK/java/jdk"

启动

在单机环境运行只须要启动bin/sqlline即可：

$ cd $WORK
$ . ./init.sh
$ ./drill/apache-drill/bin/sqlline -u jdbc:drill:zk=local
Drill log directory /var/log/drill does not exist or is not writable, defaulting to ...
Apr 06, 2015 12:47:30 AM org.glassfish.jersey.server.ApplicationHandler initialize
INFO: Initiating Jersey application, version Jersey: 2.8 2014-04-29 01:25:26...
sqlline version 1.1.6
0: jdbc:drill:zk=local>

-u jdbc:drill:zk=local表示使用本机的Drill，无需启动ZooKeeper，若是是集群环境则须要配置和启动ZooKeeper并填写地址。启动后即可以在0: jdbc:drill:zk=local>后敲入命令使用了。

试用

Drill的sample-data目录有Parquet格式的演示数据可供查询：

0: jdbc:drill:zk=local> select * from dfs.`/path/to/work/drill/apache-drill/sample-data/nation.parquet` limit 5;
+-------------+------------+-------------+------------+
| N_NATIONKEY |   N_NAME   | N_REGIONKEY | N_COMMENT  |
+-------------+------------+-------------+------------+
| 0           | ALGERIA    | 0           |  haggle. carefully f |
| 1           | ARGENTINA  | 1           | al foxes promise sly |
| 2           | BRAZIL     | 1           | y alongside of the p |
| 3           | CANADA     | 1           | eas hang ironic, sil |
| 4           | EGYPT      | 4           | y above the carefull |
+-------------+------------+-------------+------------+
5 rows selected (0.741 seconds)

这里用的库名格式为dfs.`本地文件（Parquet、JSON、CSV等文件）绝对路径`。能够看出只要熟悉SQL语法几乎没有学习成本。但Parquet格式文件须要专用工具查看、编辑，不是很方便，后续再专门介绍，下文先使用更通用的CSV和JSON文件进行演示。

在$WORK/data中建立以下test.csv文件：

1101,SteveEurich,Steve,Eurich,16,StoreT
1102,MaryPierson,Mary,Pierson,16,StoreT
1103,LeoJones,Leo,Jones,16,StoreTem
1104,NancyBeatty,Nancy,Beatty,16,StoreT
1105,ClaraMcNight,Clara,McNight,16,Store

而后查询：

0: jdbc:drill:zk=local> select * from dfs.`/path/to/work/drill/data/test.csv`;
+------------+
|  columns   |
+------------+
| ["1101","SteveEurich","Steve","Eurich","16","StoreT"] |
| ["1102","MaryPierson","Mary","Pierson","16","StoreT"] |
| ["1103","LeoJones","Leo","Jones","16","StoreTem"] |
| ["1104","NancyBeatty","Nancy","Beatty","16","StoreT"] |
| ["1105","ClaraMcNight","Clara","McNight","16","Store"] |
+------------+
5 rows selected (0.082 seconds)

能够看到结果和以前的稍有不一样，由于CSV文件没有地方存放列列名，因此统一用columns代替，若是须要具体制定列则须要用columns[n]，如：

0: jdbc:drill:zk=local> select columns[0], columns[3] from dfs.`/path/to/work/drill/data/test.csv`;
+------------+------------+
|   EXPR$0   |   EXPR$1   |
+------------+------------+
| 1101       | Eurich     |
| 1102       | Pierson    |
| 1103       | Jones      |
| 1104       | Beatty     |
| 1105       | McNight    |
+------------+------------+

CSV文件格式比较简单，发挥不出Drill的强大优点，下边更复杂的功能使用和Parquet更接近的JSON文件进行演示。

在$WORK/data中建立以下test.json文件：

{
  "ka1": 1,
  "kb1": 1.1,
  "kc1": "vc11",
  "kd1": [
    {
      "ka2": 10,
      "kb2": 10.1,
      "kc2": "vc1010"
    }
  ]
}
{
  "ka1": 2,
  "kb1": 2.2,
  "kc1": "vc22",
  "kd1": [
    {
      "ka2": 20,
      "kb2": 20.2,
      "kc2": "vc2020"
    }
  ]
}
{
  "ka1": 3,
  "kb1": 3.3,
  "kc1": "vc33",
  "kd1": [
    {
      "ka2": 30,
      "kb2": 30.3,
      "kc2": "vc3030"
    }
  ]
}

能够看到这个JSON文件内容是有多层嵌套的，结构比以前那个CSV文件要复杂很多，而查询嵌套数据正是Drill的优点所在。

0: jdbc:drill:zk=local> select * from dfs.`/path/to/work/drill/data/test.json`;
+------------+------------+------------+------------+
|    ka1     |    kb1     |    kc1     |    kd1     |
+------------+------------+------------+------------+
| 1          | 1.1        | vc11       | [{"ka2":10,"kb2":10.1,"kc2":"vc1010"}] |
| 2          | 2.2        | vc22       | [{"ka2":20,"kb2":20.2,"kc2":"vc2020"}] |
| 3          | 3.3        | vc33       | [{"ka2":30,"kb2":30.3,"kc2":"vc3030"}] |
+------------+------------+------------+------------+
3 rows selected (0.098 seconds)

select *只查出第一层的数据，更深层的数据只以本来的JSON数据呈现出来，咱们显然不该该只关心第一层的数据，具体怎么查彻底为所欲为：

0: jdbc:drill:zk=local> select sum(ka1), avg(kd1[0].kb2) from dfs.`/path/to/work/drill/data/test.json`;
+------------+------------+
|   EXPR$0   |   EXPR$1   |
+------------+------------+
| 6          | 20.2       |
+------------+------------+
1 row selected (0.136 seconds)

能够经过kd1[0]来访问嵌套到第二层的这个表。

0: jdbc:drill:zk=local> select kc1, kd1[0].kc2 from dfs.`/path/to/work/drill/data/test.json` where kd1[0].kb2 = 10.1 and ka1 = 1;
+------------+------------+
|    kc1     |   EXPR$1   |
+------------+------------+
| vc11       | vc1010     |
+------------+------------+
1 row selected (0.181 seconds)

建立view：

0: jdbc:drill:zk=local> create view dfs.tmp.tmpview as select kd1[0].kb2 from dfs.`/path/to/work/drill/data/test.json`;
+------------+------------+
|     ok     |  summary   |
+------------+------------+
| true       | View 'tmpview' created successfully in 'dfs.tmp' schema |
+------------+------------+
1 row selected (0.055 seconds)

0: jdbc:drill:zk=local> select * from dfs.tmp.tmpview;
+------------+
|   EXPR$0   |
+------------+
| 10.1       |
| 20.2       |
| 30.3       |
+------------+
3 rows selected (0.193 seconds)

能够把嵌套的第二层表打平（整合kd1[0]..kd1[n]）：

0: jdbc:drill:zk=local> select kddb.kdtable.kc2 from (select flatten(kd1) kdtable from dfs.`/path/to/work/drill/data/test.json`) kddb;
+------------+
|   EXPR$0   |
+------------+
| vc1010     |
| vc2020     |
| vc3030     |
+------------+
3 rows selected (0.083 seconds)

使用细节上和mysql仍是有所不一样的，另外涉及到多层表的复杂逻辑，要想用得驾轻就熟还须要仔细阅读官方文档并多多练习。此次先蜻蜓点水了，以后会深刻了解语法层面的特性。

参考

• Apache Drill in 10 Minutes
• Analyzing Yelp JSON Data with Apache Drill

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