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Pig, mail # user - UDF property passing


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Re: UDF property passing
Raghu Angadi 2011-07-08, 19:21
yes. that is exactly how HBaseStorage uses context.

On Fri, Jul 8, 2011 at 10:19 AM, Jeremy Hanna <[EMAIL PROTECTED]>wrote:

> In CassandraStorage, we had been using some load/store URL specific
> information (keyspace, column family names) to make the
> UDFContext.properties key unique, but with what Grant said was in the docs,
> we just wrote a patch to instead use the udf context signatures for those
> keys when setting and getting those property values.  Is that the way to go
> then?  I'm setting those as member variables and then using them later.
>
>    @Override
>    public void setUDFContextSignature(String signature)
>    {
>        this.loadSignature = signature;
>    }
>
>    /* StoreFunc methods */
>    public void setStoreFuncUDFContextSignature(String signature)
>    {
>        this.storeSignature = signature;
>     }
>
>
> On Jul 8, 2011, at 7:24 AM, Grant Ingersoll wrote:
>
> > What is the guidance here on using member variables when implementing
> UDFs and passing properties?  That is, what are the semantics for using them
> to store properties for a UDF instance?  The docs talk a lot about making
> sure that no side effects happen from multiple calls to a UDF instance, but
> it is not clear whether that means it's doing things like changing the
> Location for a given instance of a UDF or just calling it multiple times.
>  PigStorage suggests not (since it keeps a member var location), but the
> UDFContext docs suggests that one keep all state in the UDFContext under an
> appropriate signature.
> >
> > See also https://issues.apache.org/jira/browse/CASSANDRA-2869 for
> another case where this has reared it's head in an improper implementation.
> >
> > -Grant
> >
> > On Jul 7, 2011, at 3:24 AM, Jeremy Hanna wrote:
> >
> >>
> >> On Jul 6, 2011, at 11:10 PM, Raghu Angadi wrote:
> >>
> >>> On Wed, Jul 6, 2011 at 7:20 PM, Jeremy Hanna <
> [EMAIL PROTECTED]>wrote:
> >>>
> >>>>
> >>>> On Jul 6, 2011, at 12:47 PM, Dmitriy Ryaboy wrote:
> >>>>
> >>>>> I think this is the same problem we were having earlier:
> >>>>> http://hadoop.markmail.org/thread/kgxhdgw6zdmadch4
> >>>>>
> >>>>> One workaround is to use defines to explicitly create different
> >>>>> instances of your UDF, and use them separately.. it's ugly but it
> >>>>> works.
> >>>>
> >>>> Thanks Dmitriy.
> >>>>
> >>>> I tried doing something like:
> >>>> define ToCassandraBag1 org.pygmalion.udf.ToCassandraBag();
> >>>> define ToCassandraBag2 org.pygmalion.udf.ToCassandraBag();
> >>>>
> >>>
> >>> This still does not work since you can't distinguish the two. The way I
> was
> >>> thinking of doing this is to let user pass in some unique sting as a
> >>> substitute for context:
> >>>
> >>> define ToCassandraBag1 ToCassandraBag('1');
> >>> define ToCassandraBag2 ToCassandraBag('2');
> >>
> >> Ah yes.  I had misunderstood.  Thanks for the clarification.  Now the
> pig docs also make more sense in the Passing Configurations to UDFs section:
> >>
> http://pig.apache.org/docs/r0.8.1/udf.html#Passing+Configurations+to+UDFs
> >> It says:
> >> "The UDF can pass its constructor arguments, or some other identifying
> strings. This allows each instantiation of the UDF to have a different
> properties object thus avoiding name space collisions between instantiations
> of the UDF."
> >> and the HBaseStorage example was helpful to see that in action.
> >>
> >> Thanks both to Raghu and Dmitriy.
> >>
> >>>
> >>> inside the UDF, you would use this arg to make a 'contextString' (see
> >>> HBaseStorage.java for example use) to store any state.
> >>>
> >>> ideally UDFs shouldn't have to do this.. They should have the same
> context
> >>> info that is available for loaders and storage.
> >>>
> >>> Raghu.
> >>>
> >>>
> >>>>
> >>>> at the top and then using each one only once.  That still produces the
> same
> >>>> error.  I guess in this case we'll just have to require the field
> names be
> >>>> entered into the UDF and it won't introspect them.  Ah well.  Would be
> nice