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
>>>> to be able to use it but I don't really see another way around this bug
>>>> with
>>>> the shared UDF context.
>>>>
>>>>>
>>>>> D
>>>>>
>>>>> On Wed, Jul 6, 2011 at 9:42 AM, Jeremy Hanna <[email protected]>
>>>> wrote:
>>>>>> We have a UDF that introspects the output schema and gets the field
>>>> names there and use that in the exec method.
>>>>>>
>>>>>> The UDF is found here:
>>>> https://github.com/jeromatron/pygmalion/blob/master/udf/src/main/java/org/pygmalion/udf/ToCassandraBag.java
>>>>>>
>>>>>> A simple example is found here:
>>>> https://github.com/jeromatron/pygmalion/blob/master/scripts/from_to_cassandra_bag_example.pig
>>>>>>
>>>>>> It takes the relation's aliases and uses them in the output so that the
>>>> user doesn't have to specify them. However we've been noticing that if you
>>>> have more than one ToCassandraBag call in a pig script, sometimes they are
>>>> run at the same time and the key is the same in the UDF context:
>>>> cassandra.input_field_schema. So we think there is an issue there (array
>>>> out of bounds exceptions when running the script, but when running in grunt
>>>> one at a time, it doesn't do that).
>>>>>>
>>>>>> Is there a right way to do this parameter passing so that we don't get
>>>> these errors when multiple calls exist?
>>>>>>
>>>>>> We thought of using the schema hash code as a suffix (e.g.
>>>> cassandra.input_field_schema.12344321) but we don't have access to the
>>>> schema in the exec method.
>>>>>>
>>>>>> We thought of having the first parameter of the input tuple be a unique
>>>> name that the script specifies, like 'filename.relationalias' as a
>>>> convention to make them unique to the file. However in the outputSchema,
>>>> we
>>>> don't have access to the input tuple, just the schema itself, so it
>>>> couldn't
>>>> get that value in there.
>>>>>>
>>>>>> Any ideas on how to make this so it doesn't stomp on each other within
>>>> the pig script? Is there a best way to do that?
>>>>>>
>>>>>> Thanks!
>>>>>>
>>>>>> Jeremy
>>>>
>>>>
>>
>
> --------------------------
> Grant Ingersoll
>
>
>
