I will take it, hope to make some help.
Best, Danny Chan 在 2019年4月1日 +0800 PM7:20，Stamatis Zampetakis <[email protected]>，写道： > It seems that the discusion has somehow converged (at least to the major > points). I created CALCITE-2969, for whoever decides to tackle this issue. > > [1] https://issues.apache.org/jira/browse/CALCITE-2969 > > Στις Δευ, 25 Μαρ 2019 στις 8:57 μ.μ., ο/η Julian Hyde <[email protected]> > έγραψε: > > > Generally +1 on what Haisheng says. Specifically: > > > > I like the idea of renaming EnumerableCorrelate, and making it not extend > > Correlate. I would choose EnumerableNestedLoopJoin rather than > > EnumerableNestLoopJoin. > > > > Shifting from LogicalCorrelate to LogicalApply is worth considering. > > LogicalApply is similar to the “map” operator in functional programming, or > > “selectMany” in LINQ, so is very well-behaved and powerful - a good > > abstraction. > > > > Regarding SemiJoin and EquiJoin. Maybe we could deprecate them, or maybe > > we could convert them to interfaces. I’ll leave that decision to whoever > > actually writes the code. If we moved a few things to interfaces (including > > JoinLike I mentioned earlier) maybe we’d get out of the gridlock caused by > > the type hierarchy. > > > > Regarding when to decorrelate. Decorrelation during sql-to-rel is legacy. > > We now prefer to decorrelate using rules, in RelNode-land. There may be > > bugs in the legacy decorrelation and we do not aggressively fix them. We > > can even start to remove functionality if it helps us make > > SqlToRelConverter simpler. > > > > Julian > > > > > > > > > > > > > > > > > > > On Mar 25, 2019, at 12:23 PM, Haisheng Yuan <[email protected]> > > wrote: > > > > > > I agree with Stamatis that JoinRelType should have values: > > > Inner, Left (Outer), Full (Outer), Semi, Anti. > > > The option of right outer join is not necessary, because we can flip the > > inner/outer to left outer join. > > > > > > SemiJoin and EquiJoin can be deprecated. > > > > > > EnumerableCorrelate is confusing, correlate is a logical concept, better > > to rename it to EnumerableNestLoopJoin. SemiJoin can be implemented by > > nestloop, hashjoin or mergejoin. > > > I don’t see the necessity of having a separate physical operator > > EnumerableSemiJoin. > > > But these are minor naming issue. > > > > > > Regarding the LogicalCorrelate, I view it as a kind of operator similar > > to LogicalApply [1], which is > > > the logical operator in Microsoft SQL Server and Greenplum Orca > > optimizer. Both uses LogicalApply > > > operator to represent the correlated join that inner has reference to > > the outer variable. The apply may > > > have different type: cross apply (or inner apply), outer apply, semi > > apply, anti-semi apply. They are > > > just subset of join types, maybe it is why it is acciociated with > > JoinRelType, or reuse. The main > > > difference between Correlate (or Apply) and Join is (logically > > speaking): In Correlate, inner has > > > reference to outer. In Join, inner doesn’t reference outer. NestLoopJoin > > can implement both. > > > > > > With optimizer transformation rules, Correlate (or Apply) can be > > transformed into a Join, or a Join > > > is transfomed into a Correlate (Or Apply), in case there is an index can > > be used in inner relation. > > > > > > What I am not comfortable with is: > > > In SQL Server and GPDB Orca optimzier, Sql is translated into logical > > relation as it should be ( > > > keep subquery as it is), then use all kinds of apply rules to unnest > > subqueries based on cost model, > > > which seems reasonable to me. > > > But in Calcite, we can not only decorrelate in SqlToRel stage, but also > > can do it in SubqueryRemoveRule. > > > Should we unify them all in the rules and keep SqlToRelConverter simple? > > > > > > Thanks ~ > > > Haisheng Yuan > > > ------------------------------------------------------------------ > > > 发件人：Stamatis Zampetakis<[email protected]> > > > 日 期：2019年03月23日 07:31:35 > > > 收件人：<[email protected]> > > > 主 题：Re: Join, SemiJoin, Correlate > > > > > > Since we are discussing this topic I thought it would be could to bring > > > back > > > to the surface a similar discussion [1] that has been done a few years > > ago > > > in this list. > > > > > > I am leaning towards option 3 where JoinRelType has all necessary values: > > > Inner, Left, Semi, Anti, and Full. > > > With these changes it seems we could remove (deprecate) also SemiJoin, > > and > > > EquiJoin. > > > > > > On the physical level we could have: > > > 1. EnumerableCorrelate or EnumerableNestedLoopJoin; > > > 2. EnumerableMergeJoin; > > > 3. EnumerableHashJoin (currently EnumerableJoin) > > > > > > and for the above we could pass the JoinRelType throwing an exception > > when > > > the specific algorithm cannot be used to implement a specific type of > > join. > > > > > > EnumerableSemiJoin and EnumerableThetaJoin could also be removed and > > > covered from the above I think. > > > > > > Regarding Correlate and LogicalCorrelate, I am not sure what should we > > do. > > > Associating the JoinRelType with it does not seem right, and making > > > Correlate also a Join is not very attractive either. > > > > > > Best, > > > Stamatis > > > > > > [1] > > > > > http://mail-archives.apache.org/mod_mbox/calcite-dev/201411.mbox/%3CCAB%3DJe-H7AWEHbKzjrRHd-YcZgkgWzFORALrz_mMc2k7WDdj54Q%40mail.gmail.com%3E > > > > > > > > > Στις Πέμ, 21 Μαρ 2019 στις 10:35 μ.μ., ο/η Walaa Eldin Moustafa < > > > [email protected]> έγραψε: > > > > > > > > Is your concern with how we have structured the class hierarchy? Or > > just > > > > how we describe Correlate in the documentation? > > > > > > > > My concern is with both, but mainly the former. > > > > > > > > > I do agree that Correlate and nested loops joins are not the same (one > > > > is logical, the other physical). However, they have a lot in common, in > > > > particular the fact that one input sets variables and the input reads > > those > > > > variables. > > > > > > > > I think this commonality describes how the query is written, but not > > > > necessarily what it is logically equivalent to. It also describes the > > > > "how", and not necessarily the "what". I would say logical > > > > representations should be concerned with the "what" part. > > > > > > > > > I can’t think of any way to represent a nested loops join (e.g. for > > each > > > > department, find all employees in that department) that does not use > > > > variables to tie together the two inputs. And therefore I am happy with > > the > > > > fact that our Java implementation of nested-loops join is ‘class > > > > EnumerableCorrelate extends Correlate’. > > > > > > > > That is correct. The two variables are required. At the logical level > > > > they are mapped to the Correlate variables, or the Join keys after > > > > decorrelation. After going to physical, we can only have join keys. > > > > One of the keys can be the basis for the outer loop and the other for > > > > the inner loop if needed. That is true for both Correlate and Join > > > > operators. Both keys can even be used in another way than forming > > > > nested loops such as using them to implement hash or merge joins > > > > (again for regular Join or Correlate join after decorrelation). > > > > > > > > Thanks, > > > > Walaa. > > > > > > > > On Thu, Mar 21, 2019 at 2:08 PM Julian Hyde <[email protected]> wrote: > > > > > > > > > > > In addition, I would not present Correlate > > > > > > as a nested loops join. > > > > > > > > > > > > > > > Is your concern with how we have structured the class hierarchy? Or > > just > > > > how we describe Correlate in the documentation? > > > > > > > > > > I do agree that Correlate and nested loops joins are not the same (one > > > > is logical, the other physical). However, they have a lot in common, in > > > > particular the fact that one input sets variables and the input reads > > those > > > > variables. > > > > > > > > > > I can’t think of any way to represent a nested loops join (e.g. for > > each > > > > department, find all employees in that department) that does not use > > > > variables to tie together the two inputs. And therefore I am happy with > > the > > > > fact that our Java implementation of nested-loops join is ‘class > > > > EnumerableCorrelate extends Correlate’. > > > > > > > > > > > > > > > Julian > > > > > > > > > > > On Mar 21, 2019, at 1:12 PM, Walaa Eldin Moustafa < > > > > [email protected]> wrote: > > > > > > > > > > > > I would vote for number 3. In addition, I would not present > > > > > > Correlate > > > > > > as a nested loops join. Moreover, nested loops, hash and merge joins > > > > > > should be able to map to both Join or Correlate logical ones when > > > > > > possible (no inherent correlation between logical join type and > > > > > > physical types). > > > > > > > > > > > > On Thu, Mar 21, 2019 at 11:55 AM Julian Hyde <[email protected]> > > wrote: > > > > > > > > > > > > > > I have a few ideas for refactorings. (I’m not convinced by any of > > > > them, but let me know which you like.) > > > > > > > > > > > > > > 1. Get rid of SemiJoinType. It is mis-named (it is not used by > > > > SemiJoin, it is used by Correlate, but in a field called joinType). > > > > > > > > > > > > > > 2. In Correlate, use org.apache.calcite.linq4j.CorrelateJoinType. > > > > > > > It > > > > has the same set of values as SemiJoinType, but it has a better name. > > > > > > > > > > > > > > 3. Get rid of both SemiJoinType and CorrelateJoinType, and use > > > > JoinRelType for everything. We would have to add SEMI and ANTI values. > > Also > > > > some methods to find out whether the resulting row type contains fields > > > > from the left and right inputs or just the left input. > > > > > > > > > > > > > > 4. Add “interface JoinLike extends BiRel” and make Join, SemiJoin > > > > > > > and > > > > Correlate implement it. It would have a methods that say whether the LHS > > > > and RHS generate nulls, and whether the output row type contains columns > > > > from the right input. This seems attractive because it lets Join, > > SemiJoin > > > > and Correlate continue to be structurally different. > > > > > > > > > > > > > > Julian > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Mar 20, 2019, at 6:55 PM, Haisheng Yuan > > > > > > > > <[email protected]> > > > > wrote: > > > > > > > > > > > > > > > > SubPlan (in Postgres’ term) is a Postgres physical relational > > > > > > > > node > > > > to evaluate correlated subquery. What I mean is correlated subquery that > > > > can’t be decorrelated can’t be implemented by hashjoin or mergejoin. > > But it > > > > is off topic. > > > > > > > > > > > > > > > > Thanks ~ > > > > > > > > Haisheng Yuan > > > > > > > > ------------------------------------------------------------------ > > > > > > > > 发件人：Walaa Eldin Moustafa<[email protected]> > > > > > > > > 日 期：2019年03月21日 09:31:41 > > > > > > > > 收件人：<[email protected]> > > > > > > > > 抄 送：Stamatis Zampetakis<[email protected]> > > > > > > > > 主 题：Re: Re: Join, SemiJoin, Correlate > > > > > > > > > > > > > > > > Agreed with Stamatis. Currently: 1) Correlate is tied to IN, > > > > > > > > EXISTS, > > > > > > > > NOT IN, NOT EXISTS, and 2) is used as an equivalent to nested > > > > > > > > loops > > > > > > > > join. The issues here are: 1) IN, EXISTS, NOT IN, NOT EXISTS > > > > > > > > can be > > > > > > > > rewritten as semi/anti joins, and 2) nested loops join is more > > > > > > > > of a > > > > > > > > physical operator. > > > > > > > > > > > > > > > > It seems that the minimal set of logical join types are INNER, > > > > > > > > LEFT, > > > > > > > > RIGHT, OUTER, SEMI, ANTI. > > > > > > > > > > > > > > > > So I think Calciate could have one LogicalJoin operator with an > > > > > > > > attribute to specify the join type (from the above), and a > > > > > > > > number of > > > > > > > > physical join operators (hash, merge, nested loops) whose > > > > > > > > implementation details depend on the the join type. > > > > > > > > > > > > > > > > What we lose by this model is the structure of the query > > > > > > > > (whether > > > > > > > > there was a sub-plan or not), but I would say that this is > > > > > > > > actually > > > > > > > > what is desired from a logical representation -- to abstract > > > > > > > > away > > > > from > > > > > > > > how the query is written, and how it is structured, as long as > > > > > > > > there > > > > > > > > is a canonical representation. There could also be a world where > > both > > > > > > > > models coexist (Correlate first then Decorrelate but in the > > > > > > > > light of > > > > a > > > > > > > > single logical join operator?). > > > > > > > > > > > > > > > > @Haisheng, generally, a sub-plan can also be implemented using a > > > > > > > > variant of hash or merge joins as long as we evaluate the > > > > > > > > sub-plan > > > > > > > > independently (without the join predicate), but that is up to > > > > > > > > the > > > > > > > > optimizer. > > > > > > > > > > > > > > > > Thanks, > > > > > > > > Walaa. > > > > > > > > > > > > > > > > On Wed, Mar 20, 2019 at 5:23 PM Haisheng Yuan < > > > > [email protected]> wrote: > > > > > > > > > > > > > > > > > > SemiJoinType and its relationship with JoinRelType do confuse > > > > > > > > > me a > > > > little bit. > > > > > > > > > > > > > > > > > > But I don’t think we should not have LogicalCorrelate. It is > > > > > > > > > useful > > > > to represent the lateral or correlated subquery (aka SubPlan in Postgres > > > > jargon). The LogicalCorrelate can be implemented as NestLoopJoin in > > > > Calcite, or SubPlan in Postgres’s terminology, but it can’t be > > implemented > > > > as HashJoin or MergeJoin. > > > > > > > > > > > > > > > > > > Thanks ~ > > > > > > > > > Haisheng Yuan > > > > > > > > > ------------------------------------------------------------------ > > > > > > > > > 发件人：Stamatis Zampetakis<[email protected]> > > > > > > > > > 日 期：2019年03月21日 07:13:15 > > > > > > > > > 收件人：<[email protected]> > > > > > > > > > 主 题：Re: Join, SemiJoin, Correlate > > > > > > > > > > > > > > > > > > I have bumped into this quite a few times and I think we > > > > > > > > > should > > > > really try > > > > > > > > > to improve the design of the join hierarchy. > > > > > > > > > > > > > > > > > > From a logical point of view I think it makes sense to have > > > > > > > > > the > > > > following > > > > > > > > > operators: > > > > > > > > > InnerJoin, LeftOuterJoin, FullOuterJoin, SemiJoin, AntiJoin, > > > > (GroupJoin) > > > > > > > > > > > > > > > > > > Yet I have not thought thoroughly what should become a class, > > > > > > > > > and > > > > what a > > > > > > > > > property of the class (e.g., JoinRelType, SemiJoinType). > > > > > > > > > > > > > > > > > > Moreover, Correlate as it is right now, is basically a nested > > > > > > > > > loop > > > > join (as > > > > > > > > > its Javadoc also indicates). > > > > > > > > > Nested loop join is most often encountered as a physical > > > > > > > > > operator > > > > so I am > > > > > > > > > not sure if it should remain as is (in particular the > > > > LogicalCorrelate). > > > > > > > > > As we do not have HashJoin, MergeJoin, etc., operators at the > > > > logical > > > > > > > > > level, I think we should not have a NestedLoopJoin (aka., > > > > LogicalCorrelate). > > > > > > > > > There are valid reasons why Correlate was introduced in the > > > > > > > > > first > > > > place but > > > > > > > > > I think we should rethink a bit the design and the needs. > > > > > > > > > > > > > > > > > > @Julian: I do not know to what extend you would like to > > > > > > > > > rethink the > > > > > > > > > hierarchy but I have the impression that even small changes > > > > > > > > > can > > > > easily > > > > > > > > > break backward compatibility. > > > > > > > > > > > > > > > > > > > > > > > > > > > Στις Τετ, 20 Μαρ 2019 στις 8:07 μ.μ., ο/η Julian Hyde < > > > > [email protected]> > > > > > > > > > έγραψε: > > > > > > > > > > > > > > > > > > > I just discovered that Correlate, which is neither a Join > > > > > > > > > > nor a > > > > SemiJoin, > > > > > > > > > > uses SemiJoinType, but SemiJoin does not use SemiJoinType. > > > > > > > > > > > > > > > > > > > > Yuck. The Join/SemiJoin/Correlate type hierarchy needs some > > > > thought. > > > > > > > > > > > > > > > > > > > > Julian > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
