I have a requirement of changing the part file naming convention after running my PIG job. I want part-r-0000 to be userdefinedName-r-0000.
Any possible solution to that?
I am avoiding hadoop -cp and hadoop -mv commands.
Thanks
This files are created by map-reduce jobs generated by Pig. So you should configure Apache Map-reduce. The corresponding property is mapreduce.output.basename
You can define any Hadoop property directly in your pig script:
SET mapreduce.output.basename 'custom-name';
Starting the pig like this would do the same
pig -Dmapreduce.job.queuename=my-queue -Dmapreduce.output.basename=my-outputfilename;
Related
I want to run PIG in local mode, which is very easy
pig -x local file.pig
My requirement is to run PIG in local mode from OOZIE?
Is it possible as i think OOZIE will automatically launch map task first?
It's possible. When a pig script is run by Oozie, it's run as a one-map map-reduce job, which only runs the pig script, which in turn runs other map-reduce jobs (when pig is run in mapred mode).
It seems, that Pig action configuration doesn't allow running in local mode, but you can still run Pig script in local mode using shell action type. You only have to make sure, that your script, input and output data are in HDFS.
I don't think, we can run pig in local mode from oozie. Comment which Vishal wrote makes sense. In some cases, where there is lesser amount of data, Its better to go for pig in local mode. To run in local mode, you can run by writing a shell script and scheduling that in crontab.If you try this through oozie. Upto my knowledge It won't suit well , because Oozie is meant to run in HDFS.
If you want oozie to run on some data . It expects that data to be in HDFS (i.e distributed).And You must have the pig script as well in hdfs.I rembered seeing post from AlanGates where he mentioned PIG is designed to process data from/to HDFS and hive is for local to HDFS or HDFS to HDFS.
I'm having troubles understanding the relation between Hadoop and Pig.
I understand Pig's purpose is to hide the MapReduce pattern behind a scripting language, Pig Latin.
What I don't understand is how Hadoop and Pig are linked. So far, the only installation procedures seem to assume that pig is run on the same machine as the main hadoop node.
Indeed, it uses the hadoop configuration files.
Is this because pig only translates the scripts into mapreduce code and send them to hadoop ?
If that's the case, how could I configure Pig in order to make it send the scripts to a distant server ?
If not, does it mean we always need to have hadoop running within pig ?
Pig can run in two modes:
Local mode. In this mode Hadoop cluster is not used at all. All processes run in single JVM and files are read from the local filesystem. To run Pig in local mode, use the command:
pig -x local
MapReduce Mode. In this mode Pig converts scripts to MapReduce jobs and run them on Hadoop cluster. It is the default mode.
Cluster can be local or remote. Pig uses the HADOOP_MAPRED_HOME environment variable to find Hadoop installation on local machine (see Installing Pig).
If you want to connect to remote cluster, you should specify cluster parameters in the pig.properties file. Example for MRv1:
fs.default.name=hdfs://namenode_address:8020/
mapred.job.tracker=jobtracker_address:8021
You can also specify remote cluster address at the command line:
pig -fs namenode_address:8020 -jt jobtracker_address:8021
Hence, you can install Pig to any machine and connect to remote cluster. Pig includes Hadoop client, therefore you don't have to install Hadoop to use Pig.
I just started learning Hadoop and PIG (from last two days!) for one of my future project.
For experiments I've installed Hadoop (HDFS on default localhost:9000) as pseudo distributed mode and PIG (map-reduce mode).
When I initialized PIG by typing ./bin/pig command it launched GRUNT command line and I got message that pig connected with HDFS (localhost:9000), later I could successfully able to access HDFS thru pig.
I was expecting to perform some manual configuration for PIG to access HDFS (as per various internet articles).
My question is, from where PIG identified default HDFS configuration (localhost:9000)? I checked pig.properties but I didn't find anything there. I need this info as I might change default HDFS configuration in future.
BTW, I have HADOOP_HOME and PIG_HOME defined in my OS PATH variable.
When installing Pig (I assume v0.10.0) you have to tell how it will connect to the HDFS.
I don't know how you did this but generally this is done by adding the hadoop conf dir path to the PIG_CLASSPATH environment variable. You can also set HADOOP_CONF_DIR as well.
If you are starting the grunt shell Pig will locate the directory of the Hadoop configuration XMLs, and takes the value of fs.default.name (core-site.xml) and mapred.job.tracker (mapred-site.xml) , i.e: the location of the Namenode and JobTracker.
For reference you may have a look at the Pig shell script to see how env. variables are collected and evaluated.
PIG can connects to underlying HDFS in the 3 ways
1-
Pig uses HADOOP_HOME for finding the HADOOP client to Run.
your HADOOP_HOME should have been already setup in your bash_profile
export HADOOP_HOME=~/myHadoop/hadoop-2.5.2
2-
or else there might be possibility that your HADOOP_CONF_DIR has already been setup which contains the xml file for the hadoop configuration
export HADOOP_CONF_DIR=$HADOOP_HOME/etc/hadoop/
3-And if these are not setup you can also connect to underlying hdfs
by changing the pig.properties which is present under PIG_HOME/conf dir
I have been trying to find info on how to submit hadoop jobs through the command line.
I am aware of the command - hadoop jar jar-file main-class input output
There is also another command about which I am trying to find info, but havent been able to - hadoop job -submit job-file
What is a "job-file" and how do I create one? What is the basic difference between command (a.) and (b.) ? Which is a better option?
Thanks in advance.
Here is an Example of Job-file for running the wordcount Map-reduce job .
Similarly you can write job-file for your Map-Reduce jobs .
mapred.input.dir=data/file1.txt
mapred.output.dir=output
mapred.job.name=wordcount
mapred.mapper.class=edu.uci.ics.hyracks.examples.wordcount.WordCount$Map
mapred.combiner.class=edu.uci.ics.hyracks.examples.wordcount.WordCount$Reduce
mapred.reducer.class=edu.uci.ics.hyracks.examples.wordcount.WordCount$Reduce
mapred.input.format.class=org.apache.hadoop.mapred.TextInputFormat
mapred.output.format.class=org.apache.hadoop.mapred.TextOutputFormat
mapred.mapoutput.key.class=org.apache.hadoop.io.Text
mapred.mapoutput.value.class=org.apache.hadoop.io.IntWritable
mapred.output.key.class=org.apache.hadoop.io.Text
mapred.output.value.class=org.apache.hadoop.io.IntWritable
For me the "Hadoop Jar" is better coz , configuration done in job-file can be easily done in the program itself .
Thanks
Suppose I write a java program and i want to run it in Hadoop, then
where should the file be saved?
how to access it from hadoop?
should i be calling it by the following command? hadoop classname
what is the command in hadoop to execute the java file?
The simplest answers I can think of to your questions are:
1) Anywhere
2,3,4)$HADOOP_HOME/bin/hadoop jar [path_to_your_jar_file]
A similar question was asked here Executing helloworld.java in apache hadoop
It may seem complicated, but it's simpler than you might think!
Compile your map/reduce classes, and your main class into a jar. Let's call this jar myjob.jar.
This jar does not need to include the Hadoop libraries, but it should include any other dependencies you have.
Your main method should set up and run your map/reduce job, here is an example.
Put this jar on any machine with the hadoop command line utility installed.
Run your main method using the hadoop command line utility:
hadoop jar myjob.jar
Hope that helps.
where should the file be saved?
The data should be saved in "hdfs". You will want to probably load it into the cluster from your data source using something like Apache Flume. The file can be placed anywhere but most home is /user/hadoop/
how to access it from hadoop?
SSH into the hadoop cluster headnode like a standard linux server.
To list your hadoop root hdfs
hadoop fs -ls /
should i be calling it by the following command? hadoop classname
You should be using the hadoop command to access your data and run your programs, try hadoop help
what is the command in hadoop to execute the java file?
hadoop -jar MyJar.jar com.mycompany.MainDriver arg[0] arg[1] ...