As far as the underlying implementation, if they all use the same optimizations that you use in cube, then it can be LOCube. If they have their own optimizations etc (or could), it may be worth them having their own Logical operators (which might just be LOCube with flags for the time being) that allows us more flexibilty. But I suppose that's between you, eclipse, and your GSOC mentor.
2012/5/30 Prasanth J <[email protected]> > Thanks Alan and Jon for expressing your views. > > I agree with Jon's point, if the syntax contains CUBE then user expects it > to perform CUBE operation. So Jon's syntax seems more meaningful and concise > > rel = CUBE rel BY (dims); > rel = ROLLUP rel BY (dims); > rel = GROUPING_SET rel BY (dims); > > 2 reasons why I do not prefer using SQL syntax is > 1) I do not want to break into existing Group operator implementation :) > 2) The syntax gets longer in case of partial hierarchical cubing/rollups > For ex: > > rel = GROUP rel BY dim0, ROLLUP(dim1, dim2, dim3), ROLLUP(dim4,dim5,dim6), > ROLLUP(dim7,dim8,dim9); > > whereas same thing can be expressed like > > rel = ROLLUP rel BY dim0, > (dim1,dim2,dim3),(dim4,dim5,dim6),(dim7,dim8,dim9); > > Thanks Alan for pointing out the way for independently managing the > operators in parser and logical/physical plan. So for all these operators > (CUBE, ROLLUP, GROUPING_SET) I can just generate LOCube and use flags to > differentiate between these three operations. > > But, yes we are proliferating operators in this case. > > Thanks > -- Prasanth > > On May 30, 2012, at 4:42 PM, Alan Gates wrote: > > > > > On May 30, 2012, at 10:43 AM, Jonathan Coveney wrote: > > > >> I was going to say the same thing Alan said w.r.t. operators: operators > in > >> the grammar can correspond to whatever logical and physical operators > you > >> want. > >> > >> As far as the principle of least astonishment compared to SQL... Pig is > >> already pretty astonishing. I don't know why we would bend over > backwards > >> to make the syntax so similar in this case when even getting to the > point > >> of doing a CUBE means understanding an object model that is pretty > >> different from SQL. > >> > >> On that note, > >> > >> rel = CUBE rel BY GROUPING SETS(cols); > >> > >> seems really confusing. I'd much rather overload the group operating > than > >> the cube operator. If I see "cube," I expect a cube. If you start doing > >> rollups etc, that's not a cube, it's a group. Or it's just a rollup. Pig > >> latin is simple enough that I don't think having a rollup, group_set, > etc > >> operator will be so confusing, because they're already going to be > typing > >> that stuff in the conext of > >> > >> group rel by rollup(cols); and so on. I don't see how it's worth adding > >> more, confusing syntax for the sake of creating parallels with a > language > >> we now share very little with. > > > > Fair points. > > > >> > >> But I won't beat it any further... if people prefer a different syntax, > >> that's fine. Just excited to have the features in Pig! > > +1, I can live with any of the 3 syntax choices (near SQL, original, and > Jon's). > > > > Alan. > > > >> Jon > >> > >> 2012/5/30 Alan Gates <[email protected]> > >> > >>> Some thoughts on this: > >>> > >>> 1) +1 to what Dmitriy said on HAVING > >>> > >>> 2) We need to be clear about separating operators in the grammar versus > >>> logical plan versus physical plan. The choices you make in the > grammar are > >>> totally independent of the other two. That is, you could choose the > syntax: > >>> > >>> rel = GROUP rel BY CUBE (a, b, c) > >>> > >>> and still have a separate POCube operator. When the parser sees GROUP > BY > >>> CUBE it will generate an LOCube operator for the logical plan rather > than > >>> an LOGroup operator. You can still have a separate POCube physical > >>> operator. Separate optimizations can be applied to LOGroup vs. LOCube > and > >>> POGroup vs. POCube. > >>> > >>> 3) On syntax I can see arguments for keeping as close to SQL as > possible > >>> and for the syntax proposed by Prasanth. The argument for sticking > close > >>> to SQL is it conforms to the law of least astonishment. It wouldn't be > >>> exactly SQL, as it would end up looking like: > >>> > >>> rel = GROUP rel BY CUBE (cols) > >>> rel = GROUP rel BY ROLLUP (cols) > >>> rel = GROUP rel BY GROUPING SETS(cols); > >>> > >>> The argument I see for sticking with Prasanth's approach is that GROUP > is > >>> really short for COGROUP in Pig Latin, and I don't think we're > proposing > >>> doing COGROUP rel BY CUBE, nor can I see a case where you'd want to do > such > >>> a thing. This makes CUBE really a separate operation. But if we go > this > >>> route I agree with Prasanth we should do CUBE rel BY ROLLUP and CUBE > rel BY > >>> GROUPING SETS. Let's not proliferate operators. > >>> > >>> Alan. > >>> > >>> On May 29, 2012, at 3:55 PM, Prasanth J wrote: > >>> > >>>> Thanks Jonathan for looking into it and for your suggestions. > >>>> > >>>> The reason why I came with a clause rather than a separate operator > was > >>> to avoid adding additional operators to the grammar. > >>>> So adding ROLLUP, GROUPING_SET will need separate logical operators > >>> adding to the complexity. I am planning to keep everything under cube > >>> operator, so only LOCube and POCube operators will be added > additionally. > >>> And as you and Dmitriy have mentioned the purpose of HAVING clause is > the > >>> same as FILTER so we do not need a separate HAVING clause. > >>>> > >>>> I will give a quick recap of cube related operations and multiple > syntax > >>> options for achieving the same. I am also adding partial cubing and > rollup > >>> in this discussion. > >>>> > >>>> 1) CUBE > >>>> > >>>> Current syntax: > >>>> alias = CUBE rel BY (a, b); > >>>> > >>>> Following group-by's will be computed: > >>>> (a, b) > >>>> (a) > >>>> (b) > >>>> () > >>>> > >>>> 2) Partial CUBE > >>>> > >>>> Proposed syntax: > >>>> alias = CUBE rel BY a, (b, c); > >>>> > >>>> Following group-by's will be computed: > >>>> (a, b, c) > >>>> (a, b) > >>>> (a, c) > >>>> (a) > >>>> > >>>> 3) ROLLUP > >>>> > >>>> Proposed syntax 1: > >>>> alias = CUBE rel BY ROLLUP(a, b); > >>>> > >>>> Proposed syntax 2: > >>>> alias = CUBE rel BY (a::b); > >>>> > >>>> Proposed syntax 3: > >>>> alias = ROLLUP rel BY (a, b); > >>>> > >>>> Following group-by's will be computed: > >>>> (a, b) > >>>> (a) > >>>> () > >>>> > >>>> 4) Partial ROLLUP > >>>> > >>>> Proposed syntax 1: > >>>> alias = CUBE rel BY a, ROLLUP(b, c); > >>>> > >>>> Proposed syntax 2: > >>>> alias = CUBE rel BY (a, b::c); > >>>> > >>>> Proposed syntax 3: > >>>> alias = ROLLUP rel BY a, (b, c); > >>>> > >>>> Following group-by's will be computed: > >>>> (a, b, c) > >>>> (a, b) > >>>> (a) > >>>> > >>>> 5) GROUPING SETS > >>>> > >>>> Proposed syntax 1: > >>>> alias = CUBE rel BY GROUPING SETS((a), (b, c), (c)) > >>>> > >>>> Proposed syntax 2: > >>>> alias = CUBE rel BY {(a), (b, c), (c)} > >>>> > >>>> Proposed syntax 3: > >>>> alias = GROUPING_SET rel BY ((a), (b, c), (c)) > >>>> > >>>> Following group-by's will be computed: > >>>> (a) > >>>> (b, c) > >>>> (c) > >>>> > >>>> Please vote for syntax 1, 2 or 3 so that we can come to a consensus > >>> before I start hacking the grammar file. > >>>> > >>>> Thanks > >>>> -- Prasanth > >>>> > >>>> On May 29, 2012, at 4:05 PM, Jonathan Coveney wrote: > >>>> > >>>>> Hey Prashanth, happy hacking. > >>>>> > >>>>> My opinion: > >>>>> > >>>>> CUBE: > >>>>> > >>>>> alias = CUBE rel BY (a,b,c); > >>>>> > >>>>> > >>>>> I like that syntax. It's unambiguous what is going on. > >>>>> > >>>>> > >>>>> ROLLUP: > >>>>> > >>>>> > >>>>> alias = CUBE rel BY ROLLUP(a,b,c); > >>>>> > >>>>> > >>>>> I never liked that syntax in SQL. I suggest we just do what we did > with > >>> CUBE. IE > >>>>> > >>>>> > >>>>> alias = ROLLUP rel BY (a,b,c); > >>>>> > >>>>> > >>>>> GROUPING SETS: > >>>>> > >>>>> > >>>>> alias = CUBE rel BY GROUPING SETS((a,b),(b),()); > >>>>> > >>>>> > >>>>> I don't like this. The cube vs. grouping sets is confusing to me. > maybe > >>>>> following the > >>>>> same pattern you could do something like: > >>>>> > >>>>> alias = GROUPING_SET rel BY ((a,b),(b),()); > >>>>> > >>>>> As far as having, is there an optimization that can be done with a > >>> HAVING > >>>>> clause that can't be done based on the logical plan that comes > >>> afterwards? > >>>>> That seems odd to me. Since you have to materialize the result > anyway, > >>>>> can't the having clause just be a FILTER that comes after the cube? I > >>> don't > >>>>> know why we need a special syntax. > >>>>> > >>>>> My opinion. Forgive janky formatting, gmail + paste = pain. > >>>>> Jon > >>>>> > >>>>> 2012/5/27 Prasanth J <[email protected]> > >>>>> > >>>>>> Hello everyone > >>>>>> > >>>>>> I am looking for feedback from the community about the syntax for > >>>>>> CUBE/ROLLUP/GROUPING SETS operations in pig. > >>>>>> I am moving the discussion from JIRA to dev-list so that everyone > can > >>>>>> share their opinion for operator syntax. Please have a look at the > >>> syntax > >>>>>> proposal at the link below and let me know your opinion > >>>>>> > >>>>>> > >>>>>> > >>> > https://issues.apache.org/jira/browse/PIG-2167?focusedCommentId=13277644&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13277644 > >>>>>> > >>>>>> Thanks > >>>>>> -- Prasanth > >>>>>> > >>>>>> > >>>> > >>> > >>> > > > >
