On Thu, Apr 4, 2019 at 12:15 PM Lukasz Cwik <lc...@google.com> wrote:
> standard_coders.yaml[1] is where we are currently defining these formats. > Unfortunately the Python SDK has its own copy[2]. > Ah great. Thanks for the pointer. Any idea why there's a separate copy for Python ? I didn't see a significant difference in definitions looking at few random coders there but I might have missed something. If there's no reason to maintain two, we should probably unify. Also, seems like we haven't added the definition for UTF-8 coder yet. > > Here is an example PR[3] that adds the "beam:coder:double:v1" as tests to > the Java and Python SDKs to ensure interoperability. > > Robert Burke, does the Go SDK have a test where it uses > standard_coders.yaml and runs compatibility tests? > > Chamikara, creating new coder classes is a pain since the type -> coder > mapping per SDK language would select the non-well known type if we added a > new one to a language. If we swapped the default type->coder mapping, this > would still break update for pipelines forcing users to update their code > to select the non-well known type. If we don't change the default > type->coder mapping, the well known coder will gain little usage. I think > we should fix the Python coder to use the same encoding as Java for UTF-8 > strings before there are too many Python SDK users. > I was thinking that may be we should just change the default UTF-8 coder for Fn API path which is experimental. Updating Python to do what's done for Java is fine if we agree that encoding used for Java should be the standard. > > 1: > https://github.com/apache/beam/blob/master/model/fn-execution/src/main/resources/org/apache/beam/model/fnexecution/v1/standard_coders.yaml > 2: > https://github.com/apache/beam/blob/master/sdks/python/apache_beam/testing/data/standard_coders.yaml > 3: https://github.com/apache/beam/pull/8205 > > On Thu, Apr 4, 2019 at 11:50 AM Chamikara Jayalath <chamik...@google.com> > wrote: > >> >> >> On Thu, Apr 4, 2019 at 11:29 AM Robert Bradshaw <rober...@google.com> >> wrote: >> >>> A URN defines the encoding. >>> >>> There are (unfortunately) *two* encodings defined for a Coder (defined >>> by a URN), the nested and the unnested one. IIRC, in both Java and >>> Python, the nested one prefixes with a var-int length, and the >>> unnested one does not. >>> >> >> Could you clarify where we define the exact encoding ? I only see a URN >> for UTF-8 [1] while if you look at the implementations Java includes length >> in the encoding [1] while Python [1] does not. >> >> [1] >> https://github.com/apache/beam/blob/069fc3de95bd96f34c363308ad9ba988ab58502d/model/pipeline/src/main/proto/beam_runner_api.proto#L563 >> [2] >> https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/StringUtf8Coder.java#L50 >> [3] >> https://github.com/apache/beam/blob/master/sdks/python/apache_beam/coders/coders.py#L321 >> >> >> >>> >>> We should define the spec clearly and have cross-language tests. >>> >> >> +1 >> >> Regarding backwards compatibility, I agree that we should probably not >> update existing coder classes. Probably we should just standardize the >> correct encoding (may be as a comment near corresponding URN in the >> beam_runner_api.proto ?) and create new coder classes as needed. >> >> >>> >>> On Thu, Apr 4, 2019 at 8:13 PM Pablo Estrada <pabl...@google.com> wrote: >>> > >>> > Could this be a backwards-incompatible change that would break >>> pipelines from upgrading? If they have data in-flight in between operators, >>> and we change the coder, they would break? >>> > I know very little about coders, but since nobody has mentioned it, I >>> wanted to make sure we have it in mind. >>> > -P. >>> > >>> > On Wed, Apr 3, 2019 at 8:33 PM Kenneth Knowles <k...@apache.org> >>> wrote: >>> >> >>> >> Agree that a coder URN defines the encoding. I see that string UTF-8 >>> was added to the proto enum, but it needs a written spec of the encoding. >>> Ideally some test data that different languages can use to drive compliance >>> testing. >>> >> >>> >> Kenn >>> >> >>> >> On Wed, Apr 3, 2019 at 6:21 PM Robert Burke <rob...@frantil.com> >>> wrote: >>> >>> >>> >>> String UTF8 was recently added as a "standard coder " URN in the >>> protos, but I don't think that developed beyond Java, so adding it to >>> Python would be reasonable in my opinion. >>> >>> >>> >>> The Go SDK handles Strings as "custom coders" presently which for Go >>> are always length prefixed (and reported to the Runner as LP+CustomCoder). >>> It would be straight forward to add the correct handling for strings, as Go >>> natively treats strings as UTF8. >>> >>> >>> >>> >>> >>> On Wed, Apr 3, 2019, 5:03 PM Heejong Lee <heej...@google.com> wrote: >>> >>>> >>> >>>> Hi all, >>> >>>> >>> >>>> It looks like UTF-8 String Coder in Java and Python SDKs uses >>> different encoding schemes. StringUtf8Coder in Java SDK puts the varint >>> length of the input string before actual data bytes however StrUtf8Coder in >>> Python SDK directly encodes the input string to bytes value. For the last >>> few weeks, I've been testing and fixing cross-language IO transforms and >>> this discrepancy is a major blocker for me. IMO, we should unify the >>> encoding schemes of UTF8 strings across the different SDKs and make it a >>> standard coder. Any thoughts? >>> >>>> >>> >>>> Thanks, >>> >>
