So if I can summarize this thread so far, we are going to try and hammer out a types encoding spec agreeable to HBase, Phoenix, and Kite alike? As opposed to select a particular implementation today as both spec and reference implementation. Is that correct?
If so, that sounds like a promising direction. The HBase types library has the flexibility, if I understand Nick correctly, to accommodate whatever is agreed upon and we could then provide a reference implementation as a service for HBase users (or anyone) but there would be no strings attached, multiple implementations of the spec would interoperate by definition. > On May 19, 2014, at 3:20 AM, Nick Dimiduk <[email protected]> wrote: > > On Thu, May 15, 2014 at 9:32 AM, James Taylor <[email protected]>wrote: > >> @Nick - I like the abstraction of the DataType, but that doesn't solve the >> problem for non Java usage. > > > That's true. It's very much a Java construct. Likewise, Struct only codes > for semantics; there's no encoding defined there. For correct > multi-language support, we'll need to define these semantics the same way > we do the encoding details so that implementations can reproduce them > faithfully. > > I'm also a bit worried that it might become a bottleneck for implementors >> of the serialization spec as there are many different platform specific >> operations that will likely be done on the row key. We can try to get >> everything necessary in the DataType interface, but I suspect that >> implementors will need to go under-the-covers at times (rather than waiting >> for another release of the module that defines the DataType interface) - >> might become a bottleneck. > > Time will tell. DataType is just an interface, after all. If there are > things it's missing (as there surely are, for Phoenix...), it'll need to be > extended locally until these features can be pushed down into HBase. HBase > release managers have been faithful to the monthly release train, so I > think in practice dependent projects won't have to wait long. I'm content > to take this on a case-by-case basis and watch for a trend. Do you have an > alternative idea? > >> On Wed, May 14, 2014 at 5:17 PM, Nick Dimiduk <[email protected]> wrote: >> >>> On Tue, May 13, 2014 at 3:35 PM, Ryan Blue <[email protected]> wrote: >>> >>> >>>> I think there's a little confusion in what we are trying to accomplish. >>>> What I want to do is to write a minimal specification for how to store >> a >>>> set of types. I'm not trying to leave much flexibility, what I want is >>>> clarity and simplicity. >>> >>> This is admirable and was my initial goal as well. The trouble is, you >>> cannot please everyone, current users and new. So, we decided it was >> better >>> to provide a pluggable framework for extension + some basic >> implementations >>> than to implement a closed system. >>> >>> This is similar to OrderedBytes work, but a subset of it. A good example >> is >>>> that while it's possible to use different encodings (avro, protobuf, >>>> thrift, ...) it isn't practical for an application to support all of >>> those >>>> encodings. So for interoperability between Kite, Phoenix, and others, I >>>> want a set of requirements that is as small as possible. >>> >>> Minimal is good. The surface area of o.a.h.h.types is as large as it is >>> because there was always "just one more" type to support or encoding to >>> provide. >>> >>> To make the requirements small, I used off-the-shelf protobuf [1] plus a >>>> small set of memcmp encodings: ints, floats, and binary. That way, we >>> don't >>>> have to talk about how to make a memcmp Date in bytes, for example. A >>> Date >>>> is an int, which we know how to encode, and we can agree separately on >>> how >>>> to a Date is represented (e.g., Julian vs unix epoch). [2] The same >>> applies >>>> to binary, where the encoding handles sorting and nulls, but not >>> charsets. >>> >>> I think you should focus on the primitives you want to support. The >>> compound type stuff (ie, "rowkey encodings") is a can of worms because >> you >>> need to support existing users, new users, novice users, and advanced >>> users. Hence the interop between the DataType interface and the Struct >>> classes. These work together to support all of these use-cases with the >>> same basic code. For example, the protobuf encoding of postion|wire-type >> + >>> encoded value is easily implemented using Struct. >>> >>> I firmly believe that we cannot dictate rowkey composition. Applications, >>> however, are free to implement their own. By using the common DataType >>> interface, they can all interoperate. >>> >>> This is the largest reason why I didn't include OrderedBytes directly in >>>> the spec. For example, OB includes a varint that I don't think is >>> needed. I >>>> don't object to its inclusion in OB, but I think it isn't a necessary >>>> requirement for implementing this spec. >>> >>> Again, the surface area is as it is because of community consensus during >>> the first phase of implementation. That consensus disagrees with you. >>> >>> I think there are 3 things to clear up: >>>> 1. What types from OB are not included, and why? >>>> 2. Why not use OB-style structs? >>>> 3. Why choose protobuf for complex records? >>>> >>>> Does that sound like a reasonable direction to head with this >> discussion? >>> >>> Yes, sounds great! >>> >>> As far as the DataType API, I think that works great with what I'm trying >>>> to do. We'd build a DataType implementation for the encoding and the >> API >>>> will applications handle the underlying encoding. And other encoding >>>> strategies can be swapped in as well, if we want to address >> shortcomings >>> in >>>> this one, or have another for a different use case. >>> >>> I'm quite pleased to hear that. Applications like Kite, Phoenix, Kiji are >>> the target audience of the DataType API. >>> >>> Thank you for picking back up this baton. It's sat for too long. >>> >>> -n >>> >>>> On 05/13/2014 02:33 PM, Nick Dimiduk wrote: >>>> >>>>> Breaking off hackathon thread. >>>>> >>>>> The conversation around HBASE-8089 concluded with two points: >>>>> - HBase should provide support for order-preserving encodings while >>>>> not dropping support for the existing encoding formats. >>>>> - HBase is not in the business of schema management; that is a >>>>> responsibility left to application developers. >>>>> >>>>> To handle the first point, OrderedBytes is provided. For the >> supporting >>>>> the second, the DataType API is introduced. By introducing this layer >>>>> above specific encoding formats, it gives us a hook for plugging in >>>>> different implementations and for helper utilities to ship with HBase, >>>>> such as HBASE-10091. >>>>> >>>>> Things get fuzzy around complex data types: pojos, compound rowkeys (a >>>>> special case of pojo), maps/dicts, and lists/arrays. These types are >>>>> composed of other types and have different requirements based on where >>>>> in the schema they're used. Again, by falling back on the DataType >> API, >>>>> we give application developers an "out" for doing what makes the most >>>>> sense for them. >>>>> >>>>> For compound rowkeys, the Struct class is designed to fill in this >> gap, >>>>> sitting between data encoding and schema expression. It gives the >>>>> application implementer, the person managing the schema, enough >>>>> flexibility express the key encoding in terms of the component types. >>>>> These components are not limited to the simple primitives already >>>>> defined, but any DataType implementation. Order preservation is likely >>>>> important here. >>>>> >>>>> For arrays/lists, there's no implementation yet, but you can see how >> it >>>>> might be done if you have a look at struct. Order preservation may or >>>>> may not be important for arrays/list. >>>>> >>>>> The situation for maps/dicts is similar to arrays/lists. The one >>>>> complication is the case where you want to map to a column family. How >>>>> can these APIs support this thing? >>>>> >>>>> Pojos are a little more complicated. Probably Struct is sufficient for >>>>> basic cases, but it doesn't support nice features like versioning -- >>>>> these are sacrificed in favor of order preservation. Luckily, there's >>>>> plenty of tools out there for this already: Avro, MessagePack, >> Protobuf, >>>>> Thrift, &c. There's no need to reinvent the wheel here. Application >>>>> developers can implement the DataType API backed by their management >>>>> tool of choice. I created HBASE-11161 and will post a patch shortly. >>>>> >>>>> Specific comments about the Hackathon notes inline. >>>>> >>>>> Thanks, >>>>> Nick >>>> >>>> >>>> -- >>>> Ryan Blue >>>> Software Engineer >>>> Cloudera, Inc. >>
