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 >>>>
