Thanks Alexey for your explanation. That’s also what I was thinking. Parquet files already have the schema built in, so it might be feasible to infer a coder automatically (like spark parquet reader). It would be great if we have some experts chime in here. @Brian Hulette<mailto:bhule...@google.com> already mentioned that the community is working on new DataFrame APIs in Python SDK, which are based on the pandas methods and use those methods at construction time to determine the schema. I think this is very close to the schema inference we have been discussing. Not sure it will be available to Java SDK though.
Regarding BEAM-11460, looks like it may not totally solve my problem. As @Alexey Romanenko<mailto:aromanenko....@gmail.com> mentioned, we may still need to know the avro or beam schema for following operations after the parquet read. A dumb question is, with BEAM-11460, after we get a PCollection<GenericRecord> from parquet read (without the need to specify avro schema), is it possible to get the attached avro schema from a GenericRecord element of this PCollection<GenericRecord>? Really appreciate it if you can help clarify my questions. Thanks! From: Alexey Romanenko <aromanenko....@gmail.com> Reply-To: "user@beam.apache.org" <user@beam.apache.org> Date: Friday, January 8, 2021 at 4:48 AM To: "user@beam.apache.org" <user@beam.apache.org> Subject: Re: Quick question regarding ParquetIO Well, this is how I see it, let me explain. Since every PCollection is required to have a Coder to materialize the intermediate data, we need to have a coder for "PCollection<GenericRecord>" as well. If I’m not mistaken, for “GenericRecord" we used to set AvroCoder that is based on Avro (or Beam too?) schema. Actually, currently it will throw an exception if you will try to use “parseGenericRecords()” with a PCollection<GenericRecord> as output pcollection since it can’t infer a Coder based on provided “parseFn”. I guess it was done intentially in this way and I doubt that we can have a proper coder for PCollection<GenericRecord> without knowing a schema. Maybe some Avro experts here can add more on this if we can somehow overcome it. On 7 Jan 2021, at 19:44, Tao Li <t...@zillow.com<mailto:t...@zillow.com>> wrote: Alexey, Why do I need to set AvroCoder? I assume with BEAM-11460 we don’t need to specify a schema when reading parquet files to get aPCollection<GenericRecord>. Is my understanding correct? Am I missing anything here? Thanks! From: Alexey Romanenko <aromanenko....@gmail.com<mailto:aromanenko....@gmail.com>> Reply-To: "user@beam.apache.org<mailto:user@beam.apache.org>" <user@beam.apache.org<mailto:user@beam.apache.org>> Date: Thursday, January 7, 2021 at 9:56 AM To: "user@beam.apache.org<mailto:user@beam.apache.org>" <user@beam.apache.org<mailto:user@beam.apache.org>> Subject: Re: Quick question regarding ParquetIO If you want to get just a PCollection<GenericRecord> as output then you would still need to set AvroCoder, but which schema to use in this case? On 6 Jan 2021, at 19:53, Tao Li <t...@zillow.com<mailto:t...@zillow.com>> wrote: Hi Alexey, Thank you so much for this info. I will definitely give it a try once 2.28 is released. Regarding this feature, it’s basically mimicking the feature from AvroIO:https://beam.apache.org/releases/javadoc/2.26.0/org/apache/beam/sdk/io/AvroIO.html<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbeam.apache.org%2Freleases%2Fjavadoc%2F2.26.0%2Forg%2Fapache%2Fbeam%2Fsdk%2Fio%2FAvroIO.html&data=04%7C01%7Ctaol%40zillow.com%7Cdab3777011ed4b6e0ec708d8b3d3c2b5%7C033464830d1840e7a5883784ac50e16f%7C0%7C0%7C637457069377524619%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=bouNPiimOXG8wvarFt2huIJ6cd8k5c2ekp2Sd4WqPjc%3D&reserved=0> I have one more quick question regarding the “reading records of an unknown schema” scenario. In the sample code a PCollection<Foo> is being returned and the parseGenericRecords requires a parsing logic. What if I just want to get a PCollection<GenericRecord> instead of a specific class (e.g. Foo in the example)? I guess I can just skip the ParquetIO.parseGenericRecords transform? So do I still have to specify the dummy parsing logic like below? Thanks! p.apply(AvroIO.parseGenericRecords(new SerializableFunction<GenericRecord, GenericRecord >() { public Foo apply(GenericRecord record) { return record; } From: Alexey Romanenko <aromanenko....@gmail.com<mailto:aromanenko....@gmail.com>> Reply-To: "user@beam.apache.org<mailto:user@beam.apache.org>" <user@beam.apache.org<mailto:user@beam.apache.org>> Date: Wednesday, January 6, 2021 at 10:13 AM To: "user@beam.apache.org<mailto:user@beam.apache.org>" <user@beam.apache.org<mailto:user@beam.apache.org>> Subject: Re: Quick question regarding ParquetIO Hi Tao, This jira [1] looks exactly what you are asking but it was merged recently (thanks to Anant Damle for working on this!) and it should be available only in Beam 2.28.0. [1] https://issues.apache.org/jira/browse/BEAM-11460<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fissues.apache.org%2Fjira%2Fbrowse%2FBEAM-11460&data=04%7C01%7Ctaol%40zillow.com%7Cdab3777011ed4b6e0ec708d8b3d3c2b5%7C033464830d1840e7a5883784ac50e16f%7C0%7C0%7C637457069377534575%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=OSgzxc3ZpzDO71H5qgDn8cgOUrgTk3pa8r9TbbnjCWk%3D&reserved=0> Regards, Alexey On 6 Jan 2021, at 18:57, Tao Li <t...@zillow.com<mailto:t...@zillow.com>> wrote: Hi beam community, Quick question about ParquetIO<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbeam.apache.org%2Freleases%2Fjavadoc%2F2.25.0%2Forg%2Fapache%2Fbeam%2Fsdk%2Fio%2Fparquet%2FParquetIO.html&data=04%7C01%7Ctaol%40zillow.com%7Cdab3777011ed4b6e0ec708d8b3d3c2b5%7C033464830d1840e7a5883784ac50e16f%7C0%7C0%7C637457069377534575%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=U4Cma5wX8rv8ZY%2FeDRa3s%2FuSgZmgwg5iL%2FdQYs1OSpA%3D&reserved=0>. Is there a way to avoid specifying the avro schema when reading parquet files? The reason is that we may not know the parquet schema until we read the files. In comparison, spark parquet reader<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fspark.apache.org%2Fdocs%2Flatest%2Fsql-data-sources-parquet.html&data=04%7C01%7Ctaol%40zillow.com%7Cdab3777011ed4b6e0ec708d8b3d3c2b5%7C033464830d1840e7a5883784ac50e16f%7C0%7C0%7C637457069377544530%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=zAmSyGlNveyeI4aKA5GreuLxBKrwRDS0pM55CP6bzeY%3D&reserved=0> does not require such a schema specification. Please advise. Thanks a lot!
