Nested and unnested contexts are two different encodings. Can we just give them different URNs? We can even just express the length-prefixed UTF-8 as a composition of the length-prefix URN and the UTF-8 URN.
On Fri, Apr 5, 2019 at 12:38 AM Robert Bradshaw <rober...@google.com> wrote: > On Fri, Apr 5, 2019 at 12:50 AM Heejong Lee <heej...@google.com> wrote: > > > > Robert, does nested/unnested context work properly for Java? > > I believe so. It is similar to the bytes coder, that prefixes vs. not > based on the context. > > > I can see that the Context is fixed to NESTED[1] and the encode method > with the Context parameter is marked as deprecated[2]. > > > > [1]: > https://github.com/apache/beam/blob/0868e7544fd1e96db67ff5b9e70a67802c0f0c8e/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/StringUtf8Coder.java#L68 > > [2]: > https://github.com/apache/beam/blob/0868e7544fd1e96db67ff5b9e70a67802c0f0c8e/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/Coder.java#L132 > > That doesn't mean it's unused, e.g. > > > https://github.com/apache/beam/blob/release-2.12.0/sdks/java/core/src/main/java/org/apache/beam/sdk/util/CoderUtils.java#L160 > > https://github.com/apache/beam/blob/release-2.12.0/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/LengthPrefixCoder.java#L64 > > (and I'm sure there's others). > > > On Thu, Apr 4, 2019 at 3:25 PM Robert Bradshaw <rober...@google.com> > wrote: > >> > >> I don't know why there are two separate copies of > >> standard_coders.yaml--originally there was just one (though it did > >> live in the Python directory). I'm guessing a copy was made rather > >> than just pointing both to the new location, but that completely > >> defeats the point. I can't seem to access JIRA right now; could > >> someone file an issue to resolve this? > >> > >> I also think the spec should be next to the definition of the URN, > >> that's one of the reason the URNs were originally in a markdown file > >> (to encourage good documentation, literate programming style). Many > >> coders already have their specs there. > >> > >> Regarding backwards compatibility, we can't change existing coders, > >> and making new coders won't help with inference ('cause changing that > >> would also be backwards incompatible). Fortunately, I think we're > >> already doing the consistent thing here: In both Python and Java the > >> raw UTF-8 encoded bytes are encoded when used in an *unnested* context > >> and the length-prefixed UTF-8 encoded bytes are used when the coder is > >> used in a *nested* context. > >> > >> I'd really like to see the whole nested/unnested context go away, but > >> that'll probably require Beam 3.0; it causes way more confusion than > >> the couple of bytes it saves in a couple of places. > >> > >> - Robert > >> > >> On Thu, Apr 4, 2019 at 10:55 PM Robert Burke <rob...@frantil.com> > wrote: > >> > > >> > My 2cents is that the "Textual description" should be part of the > documentation of the URNs on the Proto messages, since that's the common > place. I've added a short description for the varints for example, and we > already have lenghthier format & protocol descriptions there for iterables > and similar. > >> > > >> > The proto [1] *can be* the spec if we want it to be. > >> > > >> > [1]: > https://github.com/apache/beam/blob/069fc3de95bd96f34c363308ad9ba988ab58502d/model/pipeline/src/main/proto/beam_runner_api.proto#L557 > >> > > >> > On Thu, 4 Apr 2019 at 13:51, Kenneth Knowles <k...@apache.org> wrote: > >> >> > >> >> > >> >> > >> >> On Thu, Apr 4, 2019 at 1:49 PM Robert Burke <rob...@frantil.com> > wrote: > >> >>> > >> >>> We should probably move the "java" version of the yaml file [1] to > a common location rather than deep in the java hierarchy, or copying it for > Go and Python, but that can be a separate task. It's probably non-trivial > since it looks like it's part of a java resources structure. > >> >> > >> >> > >> >> Seems like /model is a good place for this if we don't want to > invent a new language-independent hierarchy. > >> >> > >> >> Kenn > >> >> > >> >> > >> >>> > >> >>> Luke, the Go SDK doesn't currently do this validation, but it > shouldn't be difficult, given pointers to the Java and Python variants of > the tests to crib from [2]. Care would need to be taken so that Beam Go SDK > users (such as they are) aren't forced to run them, and not have the yaml > file to read. I'd suggest putting it with the integration tests [3]. > >> >>> > >> >>> I've filed a JIRA (BEAM-7009) for tracking this Go SDK side work. > [4] > >> >>> > >> >>> 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/search?q=standard_coders.yaml&unscoped_q=standard_coders.yaml > >> >>> 3: https://github.com/apache/beam/tree/master/sdks/go/test > >> >>> 4: https://issues.apache.org/jira/browse/BEAM-7009 > >> >>> > >> >>> > >> >>> On Thu, 4 Apr 2019 at 13:28, 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, >
