Nudging this issue. We need to sketch out a plan to get IPC integration tests working between the Java and C++ implementations -- what's the most expedient way we can work toward making that happen?
On Sun, May 1, 2016 at 1:02 AM, Micah Kornfield <emkornfi...@gmail.com> wrote: > s/spark/slack/g > > On Sun, May 1, 2016 at 12:58 AM, Micah Kornfield <emkornfi...@gmail.com> > wrote: >> I'm not exactly sure of my availability if I am available on spark, I >> can likely make the hangout. >> >> On Fri, Apr 29, 2016 at 4:40 PM, Wes McKinney <w...@cloudera.com> wrote: >>> I was traveling today but I can do a hangout about this next week. >>> >>> On Thu, Apr 28, 2016 at 7:53 PM, Jacques Nadeau <jacq...@apache.org> wrote: >>>> Let's do a quick hangout on this. I'd like to better understand as I'm not >>>> sure we're all talking about the same thing. >>>> >>>> On Thu, Apr 28, 2016 at 5:30 PM, Micah Kornfield <emkornfi...@gmail.com> >>>> wrote: >>>> >>>>> I'm -1 on making a new primitive type in the memory layout spec [1]. >>>>> >>>>> +1 on clarifying [2], to indicate it is expected that the "Values >>>>> array" for Utf8 and Binary types should never contain null elements. >>>>> >>>>> [1] https://github.com/apache/arrow/blob/master/format/Layout.md >>>>> [2] https://github.com/apache/arrow/blob/master/format/Message.fbs >>>>> >>>>> On Thu, Apr 28, 2016 at 3:08 PM, Wes McKinney <w...@cloudera.com> wrote: >>>>> > Bumping this conversation. >>>>> > >>>>> > I'm +0 on making VARBINARY and String (identical VARBINARY but with a >>>>> > UTF8 guarantee) primitive types in the spec. Let me know what others >>>>> > think. >>>>> > >>>>> > Thanks >>>>> > >>>>> > On Fri, Apr 22, 2016 at 6:30 PM, Wes McKinney <w...@cloudera.com> wrote: >>>>> >> On Fri, Apr 22, 2016 at 6:06 PM, Jacques Nadeau <jacq...@apache.org> >>>>> wrote: >>>>> >>> On Fri, Apr 22, 2016 at 2:42 PM, Wes McKinney <w...@cloudera.com> >>>>> wrote: >>>>> >>> >>>>> >>>> On Fri, Apr 22, 2016 at 4:56 PM, Micah Kornfield < >>>>> emkornfi...@gmail.com> >>>>> >>>> wrote: >>>>> >>>> > I like the current scheme of making String (UTF8) a primitive type >>>>> in >>>>> >>>> > regards to RPC but not modeling it as a special Array type. I >>>>> >>>> > think >>>>> >>>> > the key is formally describing how logical types map to physical >>>>> types >>>>> >>>> > either is the Flatbuffer schema or in a separate document. >>>>> >>>> > >>>>> >>>> > I think there are two use-cases here: >>>>> >>>> > 1. Reconstructing Array's off the wire. >>>>> >>>> > 2. Writing algorithms/builders to deal with specific logical types >>>>> >>>> > built on Arrays. >>>>> >>>> > >>>>> >>>> > For case 1, I think it is simpler to not special case string types >>>>> as >>>>> >>>> > primitives. Understanding that a logical String type maps to a >>>>> >>>> > List<Utf8> should be sufficient and allows us to re-use the >>>>> >>>> > serialization code for ListArrays for these types. >>>>> >>>> > >>>>> >>>> >>>>> >>>> It is simpler for the IPC serde code-path. I'll let Jacques comment >>>>> >>>> but one downside of having strings as a nested type is that there are >>>>> >>>> certain code paths (for example: Parquet-related) which deal with the >>>>> >>>> flat table case. To make a Parquet analogy, there is the special >>>>> >>>> BYTE_ARRAY primitive type, even though you could technically >>>>> >>>> represent >>>>> >>>> variable-length binary data using a repeated field and using >>>>> >>>> repetition/definition levels (but the encoding/decoding overhead for >>>>> >>>> this in Parquet is much more significant than Arrow). There may be >>>>> >>>> other reasons. >>>>> >>>> >>>>> >>> >>>>> >>> I'm a bit confused about what everyone means. I didn't actually >>>>> >>> realize >>>>> >>> that this [1] had been merged yet but I'm generally on board with how >>>>> it is >>>>> >>> constructed. >>>>> >>> >>>>> >>> With regards to the c++ implementation of the items at [1], >>>>> >>> abstracting >>>>> >>> shared physical representations out seems fine to me but I don't think >>>>> we >>>>> >>> should necessitate effective 3NF for [1]. >>>>> >>> >>>>> >>> One of the key points that I'm focused on in the Java space is that >>>>> >>> I'd >>>>> >>> like to move to an always nullable pattern. This is vastly simplifying >>>>> from >>>>> >>> a code generation, casting and complexity perspective and is a nominal >>>>> cost >>>>> >>> when using column execution. If binary and varchar are primitive types >>>>> as >>>>> >>> there there is no weird special casing of avoiding the nullability >>>>> bitmap >>>>> >>> in the case of variable width items (for the offsets). But that is an >>>>> >>> implementation detail of the Java library. >>>>> >>> >>>>> >>> So in general, I like the scheme at [1] for the concepts that we all >>>>> are >>>>> >>> talking about (as opposed to eliminating lines 67 & 68) >>>>> >>> >>>>> >>> [1] https://github.com/apache/arrow/blob/master/format/Message.fbs >>>>> >>> >>>>> >> >>>>> >> Well, the issue is that mapping of metadata onto memory layout for IPC >>>>> >> purposes, at least. You can use the List code path for arbitrary List >>>>> >> types as well as strings and binary. It sounds like either way on the >>>>> >> Java side you're going to collapse UTF8 / BINARY into a primitive so >>>>> >> that you don't have to manage a separate never-used bitmap for the >>>>> >> string/binary data. It seems useful enough to me to have a primitive >>>>> >> variable-length binary/UTF8 type but I do not feel strongly about it. >>>>> >> >>>>> >>> >>>>> >>> >>>>> >>>> > For case 2, it would be nice to utilize the type system of the host >>>>> >>>> > programming language to express the semantics of a function call >>>>> (e.g. >>>>> >>>> > ParseString(StringArray strings) vs ParseString(ListArray strings), >>>>> >>>> > but I think this can be implemented without requiring a new >>>>> primitive >>>>> >>>> > type in the spec. >>>>> >>>> > >>>>> >>>> > The more interesting thing to me is if we should have a new >>>>> primitive >>>>> >>>> > type for fixed length lists (e.g. the logical type CHAR). The >>>>> >>>> > offsets array isn't necessary in this case for random access. >>>>> >>>> > >>>>> >>>> > Also, the way the VARCHAR types (based on a comment in the C++ >>>>> >>>> > ( >>>>> https://github.com/apache/arrow/blob/master/cpp/src/arrow/type.h#L63) >>>>> >>>> > are currently described as a null terminated UTF8 is problematic. >>>>> >>>> > I >>>>> >>>> > believe null bytes are valid UTF8 characters. >>>>> >>>> >>>>> >>>> >>>>> >>>> > >>>>> >>>> >>>>> >>>> Good point, sorry about that. We probably would need to length-prefix >>>>> >>>> the values, then. >>>>> >>>> >>>>> >>> >>>>> >>> >>>>> >>> Is this an input/output interface? Arrow structures should all be 4 >>>>> byte >>>>> >>> offset based and be neither length prefixed nor null terminated. >>>>> >> >>>>> >> This was a question around the VARCHAR(k) type (which in many >>>>> >> databases is distinct from a TEXT type in which any value can be >>>>> >> arbitrary length). So if you have a VARCHAR(50), you guarantee that no >>>>> >> value exceeds 50 characters. In Arrow I suppose this is just metadata >>>>> >> because you have the offsets encoding length (pardon the jet lag). >>>>> >> Micah -- I think we can nix the `VarcharType` in the C++ code, >>>>> >> leftovers from my earliest draft implementation. >>>>> >> >>>>> >> - Wes >>>>>
