Thanks for the feedback. A couple of points here and some responses below.
* One other question is whether the Nanoseconds should actually be configurable (i.e. use milliseconds or microseconds). I would lean towards no. * I'm also still not 100% convinced we need this as a first class type in arrow or if we should be looking more closely at the Struct (in the Arrow sense) based implementation. In the future where alternative encodings are supported, this could allow for much smaller footprints for this type. The 3 > field implementation doesn't seem to have any way to represent integral > days, so I am also not sure about that one. Sorry this was an email gaffe. I intended Month (32 bit int), Day (32 bit int), Nanosecond (64 bit int). OTOH I don't really understand the point of supporting "the most > reasonable ranges for Year, Month and Nanoseconds independently". What > does it bring to encode more than one month in the nanoseconds field? I'm happy with simplicity. In the past there has been some reference to people wanting to store very large timestamps (fall out of Nanoseconds max representable value) but we've concluded that this wasn't something that we wanted to really support. On Wed, Mar 31, 2021 at 4:49 AM Antoine Pitrou <anto...@python.org> wrote: > > I would favour the following characteristics : > - support for nanoseconds (especially as other Arrow temporal types > support it) > - easy to handle (which excludes the ZetaSQL representtaion IMHO) > > OTOH I don't really understand the point of supporting "the most > reasonable ranges for Year, Month and Nanoseconds independently". What > does it bring to encode more than one month in the nanoseconds field? > You can already use the Duration type for that. > > Regards > > Antoine. > > > Le 31/03/2021 à 05:48, Micah Kornfield a écrit : > > To follow-up on this conversation I did some analysis on interval types: > > > > > https://docs.google.com/document/d/1i1E_fdQ_xODZcAhsV11Pfq27O50k679OYHXFJpm9NS0/edit > Please feel free to add more details/systems I missed. > > > > Given the disparate requirements of different systems I think the > following might make sense for official types (if there isn't consensus, I > might try to contributation extension Array implementations for them to > Java and C++/Python separately). > > > > 1. 3 fields: Year (32 bit), Month (32 bit), Nanoseconds (64 bit) all > signed. > > 2. Postgres representation (Downside is it doesn't support Nanoseconds, > only microseconds). > > 3. ZetaSQL implementation (Requires some bit manipulation) but supports > the most reasonable ranges for Year, Month and Nanoseconds independently. > > > > Thoughts? > > > > Micah > > > > On 2021/02/18 04:30:55 Micah Kornfield wrote: > >>> > >>> I didn’t find any page/documentation on how to do RFC in Arrow > protocol, > >>> so can anyone point me to it or PR with email will be enough? > >> > >> That is enough to start discussion. Before formal acceptance and > merging > >> of the PR there needs to be a Java and C++ implementations for the type > >> that pass integration tests. At the time this guideline was instituted > >> Java and C++ were considered the "reference" implementations (I think > they > >> still have the most complete integration test coverage). > >> > >> My understanding is that the current modelling of intervals mimics SQL > >> standards (e.g. SQL Server [1]). So it would also be good to step back > and > >> understand what problem DF is trying to solve and how it differs from > other > >> SQL implementations. I'd be hesitant to accept COMPLEX as a new type > >> without a much deeper analysis into calendar representations within > Arrow > >> and how they relate to other existing systems (e.g. Hive and some > >> assortment of existing SQL databases). For instance the current > modelling > >> of timestamps does not lend itself to constructing a COMPLEX interval > type > >> particularly well. (Duration was introduced for this reason). > >> > >> I think both Wes's suggestion of FixedSizeBinary and Andrew's of > composing > >> the with a struct are good stop-gaps. These obviously have different > >> trade-offs. Ultimately, it would be good to define common extension > types > >> that can represent this use-case if there really is demand for it (if it > >> doesn't become a top level type). > >> > >> [1] > >> > https://docs.microsoft.com/en-us/sql/odbc/reference/appendixes/interval-data-types?view=sql-server-ver15 > >> > >> -Micah > >> > >> On Wed, Feb 17, 2021 at 2:05 PM Andrew Lamb <al...@influxdata.com> > wrote: > >> > >>> That is a great suggestion Wes, thank you. > >>> > >>> I wonder if we could get away with a 128 bit representation that is the > >>> concatenation of the two existing interval types (YearMonth)(DayTime). > Or > >>> maybe even define a `struct` type with those fields that is used by > >>> DataFusion. > >>> > >>> Basically, given our reading of the Arrow spec[1], it is currently not > >>> possible to precisely represent an interval that has both monthly and > >>> sub-montly granularity. > >>> > >>> As Dmtry says, if you have an interval seemingly simple like 1 month, > 1 > >>> day > >>> > >>> Using IntervalUnit(YEAR_MONTH) can't represent the 1 day > >>> Using IntervalUnit(DAY_TIME) can't represent the month as different > months > >>> have different numbers of days > >>> > >>> [1] > >>> > https://github.com/apache/arrow/blob/master/format/Schema.fbs#L249-L260 > >>> > >>> > >>> On Wed, Feb 17, 2021 at 5:01 PM Wes McKinney <wesmck...@gmail.com> > wrote: > >>> > >>>> On Wed, Feb 17, 2021 at 3:46 PM <t...@dmtry.me> wrote: > >>>>> > >>>>>> It's unclear to me that this needs to be introduced into the > >>> top-level > >>>>> > >>>>> Similar thing to columnar format, How to store interval like 1 month > 1 > >>>> day 1 hour? It’s not possible to do it without converting 1 month to > 30 > >>>> days, which is a bad way. > >>>>> > >>>> > >>>> Presumably you can represent a complex interval in a fixed number of > >>>> bytes, and then embed the data in a FixedSizeBinary type. You can > >>>> adorn this type with extension type metadata so that DataFusion can > >>>> then apply Interval semantics to it. This could also serve as an > >>>> interim strategy for you to proceed with implementation while > >>>> proposing a top-level type to the Arrow format (which may or may not > >>>> be accepting) so you aren't blocked on acceptance of changes into > >>>> Schema.fbs. > >>>> > >>>>>> On 17 Feb 2021, at 21:02, Wes McKinney <wesmck...@gmail.com> wrote: > >>>>>> > >>>>>> It's unclear to me that this needs to be introduced into the > >>> top-level > >>>>>> columnar format without more analysis — have you considered > >>>>>> implementing this for DataFusion as an extension type for the time > >>>>>> being? > >>>>>> > >>>>>> On Wed, Feb 17, 2021 at 11:59 AM t...@dmtry.me <mailto: > t...@dmtry.me > >>>> > >>>> <t...@dmtry.me <mailto:t...@dmtry.me>> wrote: > >>>>>>> > >>>>>>> Hi, > >>>>>>> > >>>>>>> For now, There are only two types of IntervalUnit inside Arrow: > >>>>>>> > >>>>>>> - YearMonth - month stored as int32 > >>>>>>> - DayTime - days as int32 and time in milliseconds as in32. Total > >>>> (64 bites) > >>>>>>> > >>>>>>> Since DF is using Arrow, It’s not possible to store “Complex” > >>>> intervals such 1 MONTH 1 DAY 1 HOUR. > >>>>>>> I think, the best way to understand the problem will be to read a > >>>> comment from DF codebase: > >>>> > >>> > https://github.com/apache/arrow/blob/bca7d2fe84ccd8fc1129cb4d85448eb0779c52c3/rust/datafusion/src/sql/planner.rs#L1148 > >>>>>>> > >>>>>>> // Interval is tricky thing > >>>>>>> // 1 day is not 24 hours because timezones, 1 year != > >>> 365/364! > >>>> 30 days != 1 month > >>>>>>> // The true way to store and calculate intervals is to > store > >>>> it as it defined > >>>>>>> // Due the fact that Arrow supports only two types > YearMonth > >>>> (month) and DayTime (day, time) > >>>>>>> // It's not possible to store complex intervals > >>>>>>> // It's possible to do select (NOW() + INTERVAL '1 year') + > >>>> INTERVAL '1 day'; as workaround > >>>>>>> if result_month != 0 && (result_days != 0 || result_millis > != > >>>> 0) { > >>>>>>> return Err(DataFusionError::NotImplemented(format!( > >>>>>>> "DF does not support intervals that have both a > >>>> Year/Month part as well as Days/Hours/Mins/Seconds: {:?}. Hint: try > >>>> breaking the interval into two parts, one with Year/Month and the > other > >>>> with Days/Hours/Mins/Seconds - e.g. (NOW() + INTERVAL '1 year') + > >>> INTERVAL > >>>> '1 day'", > >>>>>>> value > >>>>>>> ))); > >>>>>>> } > >>>>>>> > >>>>>>> > >>>>>>> > >>>>>>> I prepared a PR https://github.com/apache/arrow/pull/9516/files < > >>>> https://github.com/apache/arrow/pull/9516/files> < > >>>> https://github.com/apache/arrow/pull/9516/files < > >>>> https://github.com/apache/arrow/pull/9516/files>> that introduce a > new > >>>> type for IntervalUnit called Complex, that store both YearMonth and > >>> DayTime > >>>> to support complex interval. > >>>>>>> I didn’t find any page/documentation on how to do RFC in Arrow > >>>> protocol, so can anyone point me to it or PR with email will be > enough? > >>>>>>> > >>>>>>> Thanks. > >>>>> > >>>> > >>> > >> >
