Yes and Avro has similar functionality to return a default value when the schema evolves.
Re your comment: Seems like it can handle these cases with ease? I thought the "these cases" you were referring to was the issue referencing a schema definition file at runtime, which is AvroStorage does. Thrift and Protobufs via EB don't have this issue, since they deal with it at compile time with codegen. On Mon, Apr 2, 2012 at 10:18 AM, Alex Rovner <[email protected]> wrote: > Bill, > > It would seem that you will hit the same issues though. Image you are > processing log files from an application. As your schema changes, you > certainly do not want to reprocess all the historic logs. I believe > Protobufs and Thrift handle these cases gracefully by inserting nulls into > expected columns that are not found? > > Alex > > > On Mon, Apr 2, 2012 at 1:08 AM, Bill Graham <[email protected]> wrote: > >> Elephantbird has functionality to integrate with Protobufs and Thrift but >> not Avro. When reading and writing messages of either type, EB expects >> classes to be generated via schema definitions at build-time. It doesn't >> read schemas defs at run-time to dynamically generate messages like one >> would do with Avro. Hence EB takes a different approach and doesn't have >> to >> deal with the evolving schema file in the same way as AvroStorage does. >> >> >> On Sun, Apr 1, 2012 at 9:32 AM, Alex Rovner <[email protected]> wrote: >> >> > Anyone have any experience with elephantbird? Seems like it can handle >> > these cases with ease? >> > >> > Sent from my iPhone >> > >> > On Mar 30, 2012, at 12:59 AM, Bill Graham <[email protected]> wrote: >> > >> > > In the TestAvroStorage.testRecordWithFieldSchemaFromTextWithSchemaFile >> > > there's an example: >> > > >> > > STORE avro2 INTO 'output_dir' >> > > USING org.apache.pig.piggybank.storage.avro.AvroStorage ( >> > > '{"schema_file": "/path/to/schema/file" , >> > > "field0": "def:member_id", >> > > "field1": "def:browser_id", >> > > "field3": "def:act_content" }' >> > > ); >> > > >> > > You specify the file that contains the schema, then you have to map >> the >> > > tuple fields to the name of the field in the avro schema. This mapping >> > is a >> > > drag, but it's currently required. >> > > >> > > Note that only the json-style constructor (as opposed to the string >> array >> > > appoach) supports schema_file without this uncommitted patch: >> > > https://issues.apache.org/jira/browse/PIG-2257 >> > > >> > > >> > > thanks, >> > > Bill >> > > >> > > On Thu, Mar 29, 2012 at 1:05 PM, IGZ Nick <[email protected]> >> wrote: >> > > >> > >> That's nice! Can you give me an example of how to use it? I am not >> able >> > to >> > >> figure it out from the code. The schemaManager is only used at one >> place >> > >> after that, and that is when the params contains a "field<number>" >> key. >> > I >> > >> don't understand that part. Is there a way I can call it simply like >> > STORE >> > >> xyz INTO 'abc' USING AvroStorage('schema_file=/path/to/schema/file')? >> > >> >> > >> >> > >> >> > >> On Wed, Mar 28, 2012 at 5:41 PM, Bill Graham <[email protected]> >> > wrote: >> > >> >> > >>> Yes, the schema can be in HDFS but the documentation for this is >> > lacking. >> > >>> Search for 'schema_file' here: >> > >>> >> > >>> >> > >>> >> > >> http://svn.apache.org/repos/asf/pig/trunk/contrib/piggybank/java/src/main/java/org/apache/pig/piggybank/storage/avro/AvroStorage.java >> > >>> >> > >>> and here: >> > >>> >> > >>> >> > >>> >> > >> http://svn.apache.org/repos/asf/pig/trunk/contrib/piggybank/java/src/test/java/org/apache/pig/piggybank/test/storage/avro/TestAvroStorage.java >> > >>> >> > >>> And be aware of this open JIRA: >> > >>> https://issues.apache.org/jira/browse/PIG-2257 >> > >>> >> > >>> And this closed one: >> > >>> https://issues.apache.org/jira/browse/PIG-2195 >> > >>> >> > >>> :) >> > >>> >> > >>> thanks, >> > >>> Bill >> > >>> >> > >>> >> > >>> On Wed, Mar 28, 2012 at 5:26 PM, IGZ Nick <[email protected]> >> wrote: >> > >>> >> > >>>> The schema has to be written in the script right? I don't think >> there >> > is >> > >>>> any way the schema can be in a file outside the script. That was >> the >> > >>>> messyness I was talking about. Or is there a way I can write the >> > schema in >> > >>>> a separate file? One way I see is to create and store a dummy file >> > with the >> > >>>> schema >> > >>>> >> > >>>> >> > >>>> Wed, Mar 28, 2012 at 4:19 PM, Bill Graham <[email protected]> >> > wrote: >> > >>>> >> > >>>>> The default value will be part of the new Avro schema definition >> and >> > >>>>> Avro should return it to you, so there shouldn't be any code >> > messyness with >> > >>>>> that approach. >> > >>>>> >> > >>>>> >> > >>>>> On Wed, Mar 28, 2012 at 4:01 PM, IGZ Nick <[email protected]> >> > wrote: >> > >>>>> >> > >>>>>> Ok.. you mean I can just use the newer schema to read the old >> schema >> > >>>>>> as well, by populating some default value for the missing field. >> I >> > think >> > >>>>>> that should work, messy code though! >> > >>>>>> >> > >>>>>> Thanks! >> > >>>>>> >> > >>>>>> On Wed, Mar 28, 2012 at 3:53 PM, Bill Graham < >> [email protected] >> > >wrote: >> > >>>>>> >> > >>>>>>> If you evolved your schema to just add fields, then you should >> be >> > >>>>>>> able to >> > >>>>>>> use a single schema descriptor file to read both pre- and >> > >>>>>>> post-evolved data >> > >>>>>>> objects. This is because one of the rules of new fields in Avro >> is >> > >>>>>>> that >> > >>>>>>> they have to have a default value and be non-null. AvroStorage >> > should >> > >>>>>>> pick >> > >>>>>>> that default field up for the old objects. If it doesn't, then >> > that's >> > >>>>>>> a bug. >> > >>>>>>> >> > >>>>>>> >> > >>>>>>> On Wed, Mar 28, 2012 at 3:26 PM, IGZ Nick <[email protected]> >> > >>>>>>> wrote: >> > >>>>>>> >> > >>>>>>>> @Bill, >> > >>>>>>>> I did look at the option of providing input as a parameter >> while >> > >>>>>>>> initializing AvroStorage(). But even then, I'll still need to >> > >>>>>>> change my >> > >>>>>>>> script to handle the two files because I'll still need to have >> > >>>>>>> separate >> > >>>>>>>> schemas right? >> > >>>>>>>> >> > >>>>>>>> @Stan, >> > >>>>>>>> Thanks for pointing me to it, it is a useful feature. But in my >> > >>>>>>> case, I >> > >>>>>>>> would never have two input files with different schemas. The >> input >> > >>>>>>> will >> > >>>>>>>> always have only one of the schemas, but I want my new script >> > (with >> > >>>>>>> the >> > >>>>>>>> additional column) to be able to process the old data as well, >> > even >> > >>>>>>> if the >> > >>>>>>>> input only contains data with the older schema. >> > >>>>>>>> >> > >>>>>>>> On Wed, Mar 28, 2012 at 3:00 PM, Stan Rosenberg < >> > >>>>>>> [email protected] >> > >>>>>>>>> wrote: >> > >>>>>>>> >> > >>>>>>>>> There is a patch for Avro to deal with this use case: >> > >>>>>>>>> https://issues.apache.org/jira/browse/PIG-2579 >> > >>>>>>>>> (See the attached pig example which loads two avro input files >> > >>>>>>> with >> > >>>>>>>>> different schemas.) >> > >>>>>>>>> >> > >>>>>>>>> Best, >> > >>>>>>>>> >> > >>>>>>>>> stan >> > >>>>>>>>> >> > >>>>>>>>> On Wed, Mar 28, 2012 at 4:22 PM, IGZ Nick < >> [email protected]> >> > >>>>>>> wrote: >> > >>>>>>>>>> Hi guys, >> > >>>>>>>>>> >> > >>>>>>>>>> I use Pig to process some clickstream data. I need to track a >> > >>>>>>> new >> > >>>>>>>> field, >> > >>>>>>>>> so >> > >>>>>>>>>> I added a new field to my avro schema, and changed my Pig >> script >> > >>>>>>>>>> accordingly. It works fine with the new files (which have >> that >> > >>>>>>> new >> > >>>>>>>>> column) >> > >>>>>>>>>> but it breaks when I run it on my old files which do not have >> > >>>>>>> that >> > >>>>>>>> column >> > >>>>>>>>>> in the schema (since avro stores schema in the data files >> > >>>>>>> itself). I >> > >>>>>>>> was >> > >>>>>>>>>> expecting that Pig will assume the field to be null if that >> > >>>>>>> particular >> > >>>>>>>>>> field does not exist. But now I am having to maintain >> separate >> > >>>>>>> scripts >> > >>>>>>>> to >> > >>>>>>>>>> process the old and new files. Is there any workaround this? >> > >>>>>>> Because I >> > >>>>>>>>>> figure I'll have to add new column frequently and I don't >> want >> > >>>>>>> to >> > >>>>>>>>> maintain >> > >>>>>>>>>> a separate script for each window where the schema is >> constant. >> > >>>>>>>>>> >> > >>>>>>>>>> Thanks, >> > >>>>>>>>> >> > >>>>>>>> >> > >>>>>>> >> > >>>>>>> >> > >>>>>>> >> > >>>>>>> -- >> > >>>>>>> *Note that I'm no longer using my Yahoo! email address. Please >> > email >> > >>>>>>> me at >> > >>>>>>> [email protected] going forward.* >> > >>>>>>> >> > >>>>>> >> > >>>>>> >> > >>>>> >> > >>>>> >> > >>>>> -- >> > >>>>> *Note that I'm no longer using my Yahoo! email address. Please >> email >> > >>>>> me at [email protected] going forward.* >> > >>>>> >> > >>>> >> > >>>> >> > >>> >> > >>> >> > >>> -- >> > >>> *Note that I'm no longer using my Yahoo! email address. Please >> email me >> > >>> at [email protected] going forward.* >> > >>> >> > >> >> > >> >> > > >> > > >> > > -- >> > > *Note that I'm no longer using my Yahoo! email address. Please email >> me >> > at >> > > [email protected] going forward.* >> > >> >> >> >> -- >> *Note that I'm no longer using my Yahoo! email address. Please email me at >> [email protected] going forward.* >> > > -- *Note that I'm no longer using my Yahoo! email address. Please email me at [email protected] going forward.*
