In some cases you just don't care and want to skip a couple bad records. For
example, you're writing ad hoc scripts to extract some stats.
In other cases you have a production system based on Pig and you want to have
clear metrics of the ignored data (without adding extra filtering and
complexity to your algorithm).
The idea is to be able to handle both.
What about this in the case you describe?
FOREACH FOO GENERATE Bar(*) ON_ERROR SkipMaxHandler(5);
And I would throw in as well:
DEFAULT ON_ERROR SPLIT MyHandler INTO ERRORS;
(It would need to append to the relation. ERRORS = UNION ERRORS, NEW_ERRORS ?)
Julien
On 1/18/11 10:48 AM, "Koji Noguchi" <knogu...@yahoo-inc.com> wrote:
If we're talking about couple of bad records, can we directly use skip-record
feature in mapreduce?
Koji
On 1/18/11 10:27 AM, "Julien Le Dem" <led...@yahoo-inc.com> 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 ...;
A = FOREACH FOO GENERATE Bar(*) ON_ERROR SPLIT MyHandler INTO A_ERRORS;
ErrorHandler would look a little more like EvalFunc:
public interface ErrorHandler<T> {
public T handle(IOExcetion ioe, EvalFunc evalFunc, Tuple input) throws
IOException;
public Schema outputSchema(Schema input);
}
There could be a built-in handler to output the skipped record (input: tuple,
funcname:chararray, errorMessage:chararray)
A = FOREACH FOO GENERATE Bar(*) ON_ERROR SPLIT INTO A_ERRORS;
Julien
On 1/16/11 12:22 AM, "Dmitriy Ryaboy" <dvrya...@gmail.com> 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
IOException;
}
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.
D
On Sat, Jan 15, 2011 at 11:53 PM, Santhosh Srinivasan <s...@yahoo-inc.com>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:hashut...@apache.org]
> Sent: Friday, January 14, 2011 7:35 PM
> To: u...@pig.apache.org
> 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 <s...@yahoo-inc.com>
> 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:dvrya...@gmail.com]
> > Sent: Tuesday, January 11, 2011 10:41 AM
> > To: u...@pig.apache.org
> > 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
> they happen 0.000001% of the time you can probably just ignore them, but if
> they happen in half your dataset, you want the job to tell you something is
> wrong. So this stuff gets non-trivial. If anyone wants to propose a design
> to solve this general problem, I think that would be a welcome addition.
> >
> > D
> >
> > On Tue, Jan 11, 2011 at 12:47 AM, hadoop n00b <new2h...@gmail.com>
> wrote:
> >
> >> Thanks, I sometimes get a date like 0001-01-01. This would be a valid
> >> date format, but when I try to get the seconds between this and
> >> another date, say 2011-01-01, I get an error that the value is too
> >> large to be fit into int and the process stops. Do we have something
> >> like ifError(x-y, null,x-y)? Or would I have to implement this as an
> >> UDF?
> >>
> >> Thanks
> >>
> >> On Tue, Jan 11, 2011 at 11:40 AM, Dmitriy Ryaboy <dvrya...@gmail.com>
> >> wrote:
> >>
> >> > Create a UDF that verifies the format, and go through a filtering
> >> > step first.
> >> > If you would like to save the malformated records so you can look
> >> > at them later, you can use the SPLIT operator to route the good
> >> > records to your regular workflow, and the bad records some place on
> HDFS.
> >> >
> >> > -D
> >> >
> >> > On Mon, Jan 10, 2011 at 9:58 PM, hadoop n00b <new2h...@gmail.com>
> wrote:
> >> >
> >> > > Hello,
> >> > >
> >> > > I have a pig script that uses piggy bank to calculate date
> differences.
> >> > > Sometimes, when I get a wierd date or wrong format in the input,
> >> > > the
> >> > script
> >> > > throws and error and aborts.
> >> > >
> >> > > Is there a way I could trap these errors and move on without
> >> > > stopping
> >> the
> >> > > execution?
> >> > >
> >> > > Thanks
> >> > >
> >> > > PS: I'm using CDH2 with Pig 0.5
> >> > >
> >> >
> >>
> >
>
