Pig Latin: Load multiple files from a date range (part of the directory structure)

Question

I have the following scenario-

Pig version used 0.70

Sample HDFS directory structure:

/user/training/test/20100810/<data files>
/user/training/test/20100811/<data files>
/user/training/test/20100812/<data files>
/user/training/test/20100813/<data files>
/user/training/test/20100814/<data files>

As you can see in the paths listed above, one of the directory names is a date stamp.

Problem: I want to load files from a date range say from 20100810 to 20100813.

I can pass the 'from' and 'to' of the date range as parameters to the Pig script but how do I make use of these parameters in the LOAD statement. I am able to do the following

temp = LOAD '/user/training/test/{20100810,20100811,20100812}' USING SomeLoader() AS (...);

The following works with hadoop:

hadoop fs -ls /user/training/test/{20100810..20100813}

But it fails when I try the same with LOAD inside the pig script. How do I make use of the parameters passed to the Pig script to load data from a date range?

Error log follows:

Backend error message during job submission
-------------------------------------------
org.apache.pig.backend.executionengine.ExecException: ERROR 2118: Unable to create input splits for: hdfs://<ServerName>.com/user/training/test/{20100810..20100813}
        at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigInputFormat.getSplits(PigInputFormat.java:269)
        at org.apache.hadoop.mapred.JobClient.writeNewSplits(JobClient.java:858)
        at org.apache.hadoop.mapred.JobClient.writeSplits(JobClient.java:875)
        at org.apache.hadoop.mapred.JobClient.access$500(JobClient.java:170)
        at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:793)
        at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:752)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:396)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1062)
        at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:752)
        at org.apache.hadoop.mapred.JobClient.submitJob(JobClient.java:726)
        at org.apache.hadoop.mapred.jobcontrol.Job.submit(Job.java:378)
        at org.apache.hadoop.mapred.jobcontrol.JobControl.startReadyJobs(JobControl.java:247)
        at org.apache.hadoop.mapred.jobcontrol.JobControl.run(JobControl.java:279)
        at java.lang.Thread.run(Thread.java:619)
Caused by: org.apache.hadoop.mapreduce.lib.input.InvalidInputException: Input Pattern hdfs://<ServerName>.com/user/training/test/{20100810..20100813} matches 0 files
        at org.apache.hadoop.mapreduce.lib.input.FileInputFormat.listStatus(FileInputFormat.java:231)
        at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigTextInputFormat.listStatus(PigTextInputFormat.java:36)
        at org.apache.hadoop.mapreduce.lib.input.FileInputFormat.getSplits(FileInputFormat.java:248)
        at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigInputFormat.getSplits(PigInputFormat.java:258)
        ... 14 more



Pig Stack Trace
---------------
ERROR 2997: Unable to recreate exception from backend error: org.apache.pig.backend.executionengine.ExecException: ERROR 2118: Unable to create input splits for: hdfs://<ServerName>.com/user/training/test/{20100810..20100813}

org.apache.pig.impl.logicalLayer.FrontendException: ERROR 1066: Unable to open iterator for alias test
        at org.apache.pig.PigServer.openIterator(PigServer.java:521)
        at org.apache.pig.tools.grunt.GruntParser.processDump(GruntParser.java:544)
        at org.apache.pig.tools.pigscript.parser.PigScriptParser.parse(PigScriptParser.java:241)
        at org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:162)
        at org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:138)
        at org.apache.pig.tools.grunt.Grunt.run(Grunt.java:75)
        at org.apache.pig.Main.main(Main.java:357)
Caused by: org.apache.pig.backend.executionengine.ExecException: ERROR 2997: Unable to recreate exception from backend error: org.apache.pig.backend.executionengine.ExecException: ERROR 2118: Unable to create input splits for: hdfs://<ServerName>.com/user/training/test/{20100810..20100813}
        at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.Launcher.getStats(Launcher.java:169)

Do I need to make use of a higher language like Python to capture all date stamps in the range and pass them to LOAD as a comma separated list?

cheers

Answer 1

Do I need to make use of a higher language like Python to capture all date stamps in the range and pass them to LOAD as a comma separated list?

Probably you don't - this can be done using custom Load UDF, or try rethinking you directory structure (this will work good if your ranges are mostly static).

additionally: Pig accepts parameters, maybe this would help you (maybe you could do function that will load data from one day and union it to resulting set, but I don't know if it's possible)

edit: probably writing simple python or bash script that generates list of dates (folders) is the easiest solution, you than just have to pass it to Pig, and this should work fine

Answer 2

Pig support globe status of hdfs, so I think pig can handle the pattern '/user/training/test/{20100810,20100811,20100812}', could you paste the error logs ?

Answer 3

Hi Andriyev,

I found this problem is caused by linux shell. Linux shell will help you expand {20100810..20100812} to 20100810 20100811 20100812, then you actually run command bin/hadoop fs -ls 20100810 20100811 20100812. But in the hdfs api, it won't help you to expand the expression.

Answer 4

Hi,

As zjffdu said, the path expansion is done by the shell. One common way to solve your problem is to simply use Pig parameters (which is a good way to make your script more resuable anyway):

shell:

pig -f script.pig -param input=/user/training/test/{20100810..20100812}

script.pig:

temp = LOAD '$input' USING SomeLoader() AS (...);