Question

本章说明如何在系统中下载，安装和设置Apache Pig。

先决条件

在选择Apache Pig之前，必须在系统上安装Hadoop和Java。

下载Apache Pig

首先，从以下网站下载最新版本的 Apache Pig

第1步：打开Apache Pig网站的主页。在新闻部分下，单击链接发布页面，如以下快照所示。

第2步：单击指定的链接后，您将被重定向到Apache Pig Releases页面。在此页面的“Download”部分。

第3步：然后您将被重定向到具有一组镜像的页面。选择并单击清华大学的镜像（更快一些这个镜像），如下所示。

步骤4：这些镜像将带您到Pig Releases页面。该页面包含各种版本的Apache Pig。单击其中的最新版本。

第5步：在这些文件夹中，您将获得各种发行版的Apache Pig的源文件和二进制文件。下载Apache Pig 0.17，Pig0.17.0-src.tar.gz和pig-0.17.0.tar.gz的源文件和二进制文件的tar文件。

安装Apache Pig

下载Apache Pig软件之后，请按照以下步骤在Linux环境中安装它。

第1步：在安装了Hadoop，Java和其他软件的安装目录的目录中，创建一个名为Pig的目录。（在我们的教程中，我们在名为Hadoop的用户中创建了Pig目录）。

$ mkdir Pig

第2步：提取下载的tar文件，如下所示。（我们只下载了二进制包）

$ cd Downloads/
$ tar zxvf pig-0.17.0.tar.gz

第3步：将pig-0.17.0.tar.gz文件的内容移动到之前创建的Pig目录中，如下所示。

$ mv pig-0.17.0/* /home/Hadoop/Pig/

配置Apache Pig

安装Apache Pig之后，我们必须对其进行配置。要进行配置，我们需要编辑两个文件-bashrc和pig.properties。

.bashrc文件

在.bashrc文件中，设置以下变量：

• PIG_HOME文件夹到Apache Pig的安装文件夹，
• PATH环境变量到bin文件夹，以及
• PIG_CLASSPATH环境变量到Hadoop安装的etc（配置）文件夹（包含core-site.xml，hdfs-site.xml和mapred-site.xml文件的目录）中。

export PIG_HOME = /home/Hadoop/Pig
export PATH  = $PATH:/home/Hadoop/pig/bin
export PIG_CLASSPATH = $HADOOP_HOME/conf

pig.properties文件

在Pig的conf文件夹中，我们有一个名为pig.properties的文件。在pig.properties文件中，您可以设置以下各种参数。

pig -h properties

支持以下属性：

Logging: verbose = true|false; default is false. This property is the same as -v
switch brief=true|false; default is false. This property is the same 
as -b switch debug=OFF|ERROR|WARN|INFO|DEBUG; default is INFO.             
This property is the same as -d switch aggregate.warning = true|false; default is true. 
If true, prints count of warnings of each type rather than logging each warning.       
Performance tuning: pig.cachedbag.memusage=<mem fraction>; default is 0.2 (20% of all memory).
Note that this memory is shared across all large bags used by the application.         
pig.skewedjoin.reduce.memusagea=<mem fraction>; default is 0.3 (30% of all memory).
Specifies the fraction of heap available for the reducer to perform the join.
pig.exec.nocombiner = true|false; default is false.
Only disable combiner as a temporary workaround for problems.         
opt.multiquery = true|false; multiquery is on by default.
Only disable multiquery as a temporary workaround for problems.
opt.fetch=true|false; fetch is on by default.
Scripts containing Filter, Foreach, Limit, Stream, and Union can be dumped without MR jobs.         
pig.tmpfilecompression = true|false; compression is off by default.             
Determines whether output of intermediate jobs is compressed.         
pig.tmpfilecompression.codec = lzo|gzip; default is gzip.
Used in conjunction with pig.tmpfilecompression. Defines compression type.         
pig.noSplitCombination = true|false. Split combination is on by default.
Determines if multiple small files are combined into a single map.         
pig.exec.mapPartAgg = true|false. Default is false.             
Determines if partial aggregation is done within map phase, before records are sent to combiner.         
pig.exec.mapPartAgg.minReduction=<min aggregation factor>. Default is 10.             
If the in-map partial aggregation does not reduce the output num records by this factor, it gets disabled.
Miscellaneous: exectype = mapreduce|tez|local; default is mapreduce. This property is the same as -x switch
pig.additional.jars.uris=<comma seperated list of jars>. Used in place of register command.
udf.import.list=<comma seperated list of imports>. Used to avoid package names in UDF.
stop.on.failure = true|false; default is false. Set to true to terminate on the first error.         
pig.datetime.default.tz=<UTC time offset>. e.g. +08:00. Default is the default timezone of the host.
Determines the timezone used to handle datetime datatype and UDFs.
Additionally, any Hadoop property can be specified.

验证安装

通过键入version命令来验证Apache Pig的安装。如果安装成功，您将获得如下所示的Apache Pig版本。

$ pig –version
Apache Pig version 0.17.0 (r1682971)  
compiled Jun 01 2015, 11:44:35