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 >>>
