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The following page has been changed by SanthoshSrinivasan:
http://wiki.apache.org/pig/PigErrorHandling

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  === Error reporting ===
  
- Provide users with readable error messages. Stack traces provide a good 
mechanism to help debugging but do not mean much to the user. Readable and 
simple error messages will be presented on STDERR. Error codes will be devised 
for common error messages. Detailed information like stack trace will be logged 
into client side logs. Users can send logs that contain the details of the 
error like stack trace to assist developers in resolving issues.
+ Provide users with readable error messages. Stack traces provide a good 
mechanism to help debugging but do not mean much to the user. Readable and 
simple error messages will be presented on STDERR. Error codes will be devised 
for all error messages. Detailed information like stack trace will be logged 
into client side logs. The logs will be stored in the current working directory 
or the user's home directory. Users can send logs that contain the details of 
the error like stack trace to assist developers in resolving issues.
  
  '''Note:''' 
  
   1. Users are responsible for purging error logs
   2. Users will be able switch on/off the detailed error messages on STDERR.
-  3. Since Pig depends on Hadoop for execution, Hadoop error messages will be 
reported by Pig. An error during execution due to a bug in Pig will be shown 
differently from that of an error in Hadoop itself.
+  3. Since Pig depends on Hadoop for execution, Hadoop error messages will be 
reported by Pig. An error during execution due to a bug in Pig will be shown 
differently from that of an error in Hadoop itself. The error code and the 
error message will indicate that the error was due to Hadoop.
  
  
  === Warning message aggregation ===
  
- With the introduction of types and NULLs into Pig, there are several 
scenarios where Pig warns the user about introduction of casts, divide by zero 
uses, etc. The warning messages are issued on each occurrence of the warning. 
While this message is useful, the increased frequency of the messages is 
annoying and distracts the user from possible error messages. In order to 
alleviate this problem, warning message aggregation will be supported to report 
the warning message and the number of occurrences of the warning message.
+ With the introduction of types and NULLs into Pig, there are several 
scenarios where Pig warns the user about introduction of casts, divide by zero 
uses, etc. The warning messages are issued on each occurrence of the warning. 
While this message is useful, the increased frequency of the messages is 
annoying and distracts the user from possible error messages. In order to 
alleviate this problem, warning message aggregation will be supported to report 
the warning message and the number of occurrences of the warning message. The 
warning message and the frequency of each warning message will be presented on 
STDERR. The logs will also contain the same information. The location of the 
log file will be the same as that of the error log file.
+ 
+ E.g.: 
+ 
+ Warning: Divide by zero: 30 times
+ 
+ Implicit cast to integer: 12 times
  
  '''Note:'''
  
-  1. Users will be able switch to turn on/off warning message aggregation
+  1. Users will be able switch to turn on/off warning message aggregation. 
Turning warning message aggregation will result in one warning message per 
warning.
  
  
  == References ==

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