Impala - Shell

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在前面的章节中，我们已经看到了使用 Cloudera 安装 Impala 及其架构。

• Impala Shell（命令提示符）
• Hue（用户界面）
• ODBC 和 JDBC（第三方库）

本章解释如何启动 Impala Shell 以及 Shell 的各种选项。

Impala Shell 命令参考

Impala Shell 的命令分为通用命令、查询特定选项和表和数据库特定选项，如下所述。

通用命令

• help
• version
• history
• shell (或) !
• connect
• exit | quit

查询特定选项

• Set/unset
• Profile
• Explain

表和数据库特定选项

• Alter
• describe
• drop
• insert
• select
• show
• use

启动 Impala Shell

打开 Cloudera 终端，以超级用户身份登录，并输入cloudera作为密码，如下所示。

[cloudera@quickstart ~]$ su
Password: cloudera
[root@quickstart cloudera]#

通过输入以下命令启动 Impala Shell：

[root@quickstart cloudera] # impala-shell 
Starting Impala Shell without Kerberos authentication 
Connected to quickstart.cloudera:21000 
Server version: impalad version 2.3.0-cdh5.5.0 RELEASE 
(build 0c891d79aa38f297d244855a32f1e17280e2129b)
********************************************************************* 

Welcome to the Impala shell. Copyright (c) 2015 Cloudera, Inc. All rights reserved.
(Impala Shell v2.3.0-cdh5.5.0 (0c891d7) built on Mon Nov 9 12:18:12 PST 2015)

Want to know what version of Impala you're connected to? Run the VERSION command to 
find out! 
********************************************************************* 
[quickstart.cloudera:21000] >

Impala - 通用命令

下面解释 Impala 的通用命令：

help 命令

Impala Shell 的help命令会列出 Impala 中可用的命令：

[quickstart.cloudera:21000] > help;
 
Documented commands (type help <topic>):
========================================================
compute  describe  insert  set     unset  with  version
connect  explain   quit    show    values use
exit     history   profile select  shell  tip 
  
Undocumented commands:
========================================= 
alter create desc drop help load summary

version 命令

version命令显示当前的 Impala 版本，如下所示。

[quickstart.cloudera:21000] > version;
Shell version: Impala Shell v2.3.0-cdh5.5.0 (0c891d7) built on Mon Nov 9 
12:18:12 PST 2015

Server version: impalad version 2.3.0-cdh5.5.0 RELEASE (build 
0c891d79aa38f297d244855a32f1e17280e2129b)

history 命令

Impala 的history命令显示 Shell 中执行的最后 10 个命令。以下是history命令的示例。在这里，我们执行了 5 个命令，即 version、help、show、use 和 history。

[quickstart.cloudera:21000] > history;
[1]:version;
[2]:help;
[3]:show databases;
[4]:use my_db;
[5]:history;

quit/exit 命令

可以使用quit或exit命令退出 Impala Shell，如下所示。

[quickstart.cloudera:21000] > exit; 
Goodbye cloudera

connect 命令

connect命令用于连接到给定的 Impala 实例。如果您没有指定任何实例，则它将连接到默认端口21000，如下所示。

[quickstart.cloudera:21000] > connect; 
Connected to quickstart.cloudera:21000 
Server version: impalad version 2.3.0-cdh5.5.0 RELEASE (build 
0c891d79aa38f297d244855a32f1e17280e2129b)

Impala 查询特定选项

Impala 的查询特定命令接受查询。它们解释如下：

Explain

explain命令返回给定查询的执行计划。

[quickstart.cloudera:21000] > explain select * from sample;
Query: explain select * from sample
+------------------------------------------------------------------------------------+ 
| Explain String                                                                     | 
+------------------------------------------------------------------------------------+ 
| Estimated Per-Host Requirements: Memory = 48.00MB VCores = 1                       | 
| WARNING: The following tables are missing relevant table and/or column statistics. |
| my_db.customers                                                                    | 
| 01:EXCHANGE [UNPARTITIONED]                                                        | 
| 00:SCAN HDFS [my_db.customers]                                                     | 
| partitions = 1/1 files = 6 size = 148B                                             | 
+------------------------------------------------------------------------------------+ 
Fetched 7 row(s) in 0.17s

Profile

profile命令显示有关最近查询的低级信息。此命令用于诊断和性能调整查询。以下是profile命令的示例。在这种情况下，profile命令返回explain查询的低级信息。

[quickstart.cloudera:21000] > profile;

Query Runtime Profile: 
Query (id=164b1294a1049189:a67598a6699e3ab6): 

   Summary: 
      Session ID: e74927207cd752b5:65ca61e630ad3ad
      Session Type: BEESWAX 
      Start Time: 2016-04-17 23:49:26.08148000 End Time: 2016-04-17 23:49:26.2404000 
      Query Type: EXPLAIN 
      Query State: FINISHED 
      Query Status: OK 
      Impala Version: impalad version 2.3.0-cdh5.5.0 RELEASE (build 0c891d77280e2129b) 
      User: cloudera 
      Connected User: cloudera 
      Delegated User: 
      Network Address:10.0.2.15:43870 
      Default Db: my_db 
      Sql Statement: explain select * from sample 
      Coordinator: quickstart.cloudera:22000 
      : 0ns 
      Query Timeline: 167.304ms 
         - Start execution: 41.292us (41.292us) - Planning finished: 56.42ms (56.386ms) 
         - Rows available: 58.247ms (1.819ms) 
         - First row fetched: 160.72ms (101.824ms) 
         - Unregister query: 166.325ms (6.253ms)
         
   ImpalaServer: 
      - ClientFetchWaitTimer: 107.969ms 
      - RowMaterializationTimer: 0ns

表和数据库特定选项

下表列出了 Impala 中的表和数据特定选项。