Hi, On Sun, Dec 16, 2018 at 4:43 AM Wenchen Fan <cloud0...@gmail.com> wrote:
> Shall we include Parquet and ORC? If they don't support it, it's hard for > general query engines like Spark to support it. For each of the more explicit timestamp types we propose a single semantics regardless of the file format. Query engines and other applications must explicitly support the new semantics, but it is not strictly necessary to extend or modify the file formats themselves, since users can declare the desired semantics directly in the end-user applications: - In SQL they would do so by using the more explicit timestamp types as detailed in the proposal. And since the SQL engines in question share the same metastore, users only have to define/update the SQL schema once to achieve interoperability in SQL. - Other applications will have to add support for the different semantics, but due to the large number of such applications, we can not coordinate all of that effort. Hopefully though, if we add support in the three major Hadoop SQL engines, other applications will follow suit. - Spark, specifically, falls into both of the categories mentioned above. It supports SQL queries, where it gets the benefit of the SQL schemas shared via the metastore. It also supports reading data files directly, where the correct timestamp semantics to use would have to be declared programmatically by the user/consumer of the API. That being said, although not strictly necessary, it is beneficial to store the semantics in some file-level metadata as well. This allows writers to record the intended semantics of timestamps and readers to recognize it, so no input is needed from the user when data is ingested from or exported to other tools. It will still require explicit support from the applications though. Parquet does have such metadata about the timestamp semantics: the isAdjustedToUTC field is part of the new parametric timestamp logical type. True means Instant semantics, while false means LocalDateTime semantics. I support the idea of adding similar metadata to other file formats as well, but I consider that to be a second step. First I would like to reach an agreement in how different SQL timestamp types should behave. (Until we follow this up with that second step, file formats with a single non-parametric timestamp type can store arbitrary semantics too, users just have to be aware of what timestamp semantics were used when they create a SQL table over the data or read it in non-SQL applications. Alternatively, we may limit the new types to file formats with timestamp semantics metadata and postpone support for other file formats until semantics metadata is added to them.) Br, Zoltan > > On Wed, Dec 12, 2018 at 3:36 AM Li Jin <ice.xell...@gmail.com> wrote: >> >> Of course. I added some comments in the doc. >> >> On Tue, Dec 11, 2018 at 12:01 PM Imran Rashid <im...@therashids.com> wrote: >>> >>> Hi Li, >>> >>> thanks for the comments! I admit I had not thought very much about python >>> support, its a good point. But I'd actually like to clarify one thing >>> about the doc -- though it discusses java types, the point is actually >>> about having support for these logical types at the SQL level. The doc >>> uses java names instead of SQL names just because there is so much >>> confusion around the SQL names, as they haven't been implemented >>> consistently. Once there is support for the additional logical types, then >>> we'd absolutely want to get the same support in python. >>> >>> Its great to hear there are existing python types we can map each behavior >>> to. Could you add a comment on the doc on each of the types, mentioning >>> the equivalent in python? >>> >>> thanks, >>> Imran >>> >>> On Fri, Dec 7, 2018 at 1:33 PM Li Jin <ice.xell...@gmail.com> wrote: >>>> >>>> Imran, >>>> >>>> Thanks for sharing this. When working on interop between Spark and >>>> Pandas/Arrow in the past, we also faced some issues due to the different >>>> definitions of timestamp in Spark and Pandas/Arrow, because Spark >>>> timestamp has Instant semantics and Pandas/Arrow timestamp has either >>>> LocalDateTime or OffsetDateTime semantics. (Detailed discussion is in the >>>> PR: https://github.com/apache/spark/pull/18664#issuecomment-316554156.) >>>> >>>> For one I am excited to see this effort going but also would love to see >>>> interop of Python to be included/considered in the picture. I don't think >>>> it adds much to what has already been proposed already because Python >>>> timestamps are basically LocalDateTime or OffsetDateTime. >>>> >>>> Li >>>> >>>> >>>> >>>> On Thu, Dec 6, 2018 at 11:03 AM Imran Rashid >>>> <iras...@cloudera.com.invalid> wrote: >>>>> >>>>> Hi, >>>>> >>>>> I'd like to discuss the future of timestamp support in Spark, in >>>>> particular with respect of handling timezones in different SQL types. >>>>> In a nutshell: >>>>> >>>>> * There are at least 3 different ways of handling the timestamp type >>>>> across timezone changes >>>>> * We'd like Spark to clearly distinguish the 3 types (it currently >>>>> implements 1 of them), in a way that is backwards compatible, and also >>>>> compliant with the SQL standard. >>>>> * We'll get agreement across Spark, Hive, and Impala. >>>>> >>>>> Zoltan Ivanfi (Parquet PMC, also my coworker) has written up a detailed >>>>> doc, describing the problem in more detail, the state of various SQL >>>>> engines, and how we can get to a better state without breaking any >>>>> current use cases. The proposal is good for Spark by itself. We're also >>>>> going to the Hive & Impala communities with this proposal, as its better >>>>> for everyone if everything is compatible. >>>>> >>>>> Note that this isn't proposing a specific implementation in Spark as yet, >>>>> just a description of the overall problem and our end goal. We're going >>>>> to each community to get agreement on the overall direction. Then each >>>>> community can figure out specifics as they see fit. (I don't think there >>>>> are any technical hurdles with this approach eg. to decide whether this >>>>> would be even possible in Spark.) >>>>> >>>>> Here's a link to the doc Zoltan has put together. It is a bit long, but >>>>> it explains how such a seemingly simple concept has become such a mess >>>>> and how we can get to a better state. >>>>> >>>>> https://docs.google.com/document/d/1gNRww9mZJcHvUDCXklzjFEQGpefsuR_akCDfWsdE35Q/edit#heading=h.dq3b1mwkrfky >>>>> >>>>> Please review the proposal and let us know your opinions, concerns and >>>>> suggestions. >>>>> >>>>> thanks, >>>>> Imran --------------------------------------------------------------------- To unsubscribe e-mail: dev-unsubscr...@spark.apache.org
