I have to actually say that a collection of test cases is not a definition of a format. It is one of the pieces, and the other one is a textual description in a prominent, discoverable place.
Kenn On Thu, Apr 4, 2019 at 1:28 PM Lukasz Cwik <lc...@google.com> wrote: > > > On Thu, Apr 4, 2019 at 1:15 PM Chamikara Jayalath <chamik...@google.com> > wrote: > >> >> >> 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. >> >> > Not certain as well. I did notice the timer coder definition didn't exist > in the Python copy. > > >> >>> 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. >> >> > That is a good idea to use the Fn API experiment to control which gets > selected. > > >> >>> 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, >>>>> >>>>
