Let's start by creating a simple usecase. For example, I would start with nullable 4 byte integer, maybe and use the example of java > (col1) > python (or c++) > (newcol) > java that is one what I'd call a single batch algorithm (e.g. one batch of values in, one out).
A simple way to sidestep the memory management/reference counting issues initially is for java to preallocate the output location for newcol for the python (or c++) code. On Wed, May 25, 2016 at 1:25 PM, Micah Kornfield <emkornfi...@gmail.com> wrote: > Just to follow-up on this. I got distracted on a few other items on > the C++ implementation side, but my next task is to get a String types > working for the C++ IPC unit test. Once I send a PR for that, it > might help clarify the concerns on both sides and we can hammer out > the details from there. > > Sound reasonable? > > -Micah > > On Fri, May 13, 2016 at 10:33 AM, Wes McKinney <wesmck...@gmail.com> > wrote: > > 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 > >>>>>> >
