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Pig >> mail # dev >> Re: Exception Handling in Pig Scripts

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Re: Exception Handling in Pig Scripts
If we're talking about couple of  bad records, can we directly use skip-record feature in mapreduce?

On 1/18/11 10:27 AM, "Julien Le Dem" <[EMAIL PROTECTED]> wrote:

That would be nice.
Also letting the error handler output the result to a relation would be useful.
(To let the script output application error metrics)
For example it could (optionally) use the keyword INTO just like the SPLIT operator.

FOO = LOAD ...;

ErrorHandler would look a little more like EvalFunc:

public interface ErrorHandler<T> {

  public T handle(IOExcetion ioe, EvalFunc evalFunc, Tuple input) throws

public Schema outputSchema(Schema input);


There could be a built-in handler to output the skipped record (input: tuple, funcname:chararray, errorMessage:chararray)



On 1/16/11 12:22 AM, "Dmitriy Ryaboy" <[EMAIL PROTECTED]> wrote:

I was thinking about this..

We add an optional ON_ERROR clause to operators, which allows a user to
specify error handling. The error handler would be a udf that would
implement an interface along these lines:

public interface ErrorHandler {

  public void handle(IOExcetion ioe, EvalFunc evalFunc, Tuple input) throws


I think this makes sense not to make a static method so that users could
keep required state, and for example have the handler throw its own
IOException of it's been invoked too many times.

On Sat, Jan 15, 2011 at 11:53 PM, Santhosh Srinivasan <[EMAIL PROTECTED]>wrote:

> Thanks for the clarification Ashutosh.
> Implementing this in the user realm is tricky as Dmitriy states.
> Sensitivity to error thresholds will require support from the system. We can
> probably provide a taxonomy of records (good, bad, incomplete, etc.) to let
> users classify each record. The system can then track counts of each record
> type to facilitate the computation of thresholds. The last part is to allow
> users to specify thresholds and appropriate actions (interrupt, exit,
> continue, etc.). A possible mechanism to realize this is the
> ErrorHandlingUDF described by Dmitriy.
> Santhosh
> -----Original Message-----
> From: Ashutosh Chauhan [mailto:[EMAIL PROTECTED]]
> Sent: Friday, January 14, 2011 7:35 PM
> Subject: Re: Exception Handling in Pig Scripts
> Santhosh,
> The way you are proposing, it will kill the pig script. I think what user
> wants is to ignore few "bad records" and to process the rest and get
> results. Problem here is how to let user tell Pig the definition of "bad
> record" and how to let him specify threshold for % of bad records at which
> Pig should fail the script.
> Ashutosh
> On Fri, Jan 14, 2011 at 18:18, Santhosh Srinivasan <[EMAIL PROTECTED]>
> wrote:
> > Sorry about the late response.
> >
> > Hadoop n00b is proposing a language extension for error handling, similar
> to the mechanisms in other well known languages like C++, Java, etc.
> >
> > For now, can't the error semantics be handled by the UDF? For exceptional
> scenarios you could throw an ExecException with the right details. The
> physical operator that handles the execution of UDF's traps it for you and
> propagates the error back to the client. You can take a look at any of the
> builtin UDFs to see how Pig handles it internally.
> >
> > Santhosh
> >
> > -----Original Message-----
> > From: Dmitriy Ryaboy [mailto:[EMAIL PROTECTED]]
> > Sent: Tuesday, January 11, 2011 10:41 AM
> > Subject: Re: Exception Handling in Pig Scripts
> >
> > Right now error handling is controlled by the UDFs themselves, and there
> is no way to direct it externally.
> > You can make an ErrorHandlingUDF that would take a udf spec, invoke it,
> trap errors, and then do the specified error handling behavior.. that's a
> bit ugly though.
> >
> > There is a problem with trapping general exceptions of course, in that if