To Stamatis,
Not exactly. My initial thought was giving the physical operator the abiity to
customize and fully control physical property derivation strategy, thus can
further help the purpose driven trait request. But since we agree to think more
high-level API to support on-demand traitset request, I will illustrate what
API is expected from implentator's perspective.
Jingfeng gave us basic steps on how the plan might be generated using top-down
purpose driven only manner, I think differently with the first several steps.
SELECT DISTINCT c, b FROM
( SELECT R.c c, S.b b FROM R, S
WHERE R.a=S.a and R.b=S.b and R.c=S.c) t;
Aggregate . (c, b)
+--- MergeJoin . (a, b, c)
|--- TableScan on R
+-- TableScan on S
1. Aggreate require collation (c,b) from its child, not permutation.
2. MergeJoin's parent require (c,b), it has 2 options. Pass it down, or ignore
it.
a) Pass down. it has join condition on (a,b,c), the required columns can be
coverd by join condition columns, so MergeJoin will try to deliver (c,b,a), and
both children must exact match. Then we will have sort on both children of
MergeJoin.
b) Ignore it. Require its first child collation on (a,b,c), but matching
type is subset. R delivers (c,b,a). Then using the first child's derived
collation trait to require its second child to exact match. Thus we have a sort
on S, and a sort on top of MergeJoin.
Both plan might be good or bad. If R, S are large, but the join result is
small, plan b) might be better, otherwise plan a) might be better.
Anyway, I hope the physical operators can have full control the physical
properties requests and derivation, in physical operator class itself, not
rules, not other places.
Per our experience, we have spent too much time on writing code for dealing
with all kinds of property requirement and derivation. But in fact, life should
be easier. I would like to the physical operator provides the following API,
and the 3rd party implementator just need to override/implement them, no more
need to be taken care.
1. void setDistributionRequests(int numReq)
Each operator can specify how many optimzation requests on some trait it want
to do. e.g. HashJoin may request the following distribution on both children:
- (hash distribution on key1, hash distribution on key1)
- (hash distribution on key2, hash distribution on key2)
- (hash distribution on all keys, hash distribution on all keys)
- (Any, Broadcast)
- (Gather, Gather)
2. RelDistribution requiredDistribution(RelDistribution required, int child)
//same for collation
Given the required distribution from parent operator, returns the required
distribution for its nth child.
3. RelDistribution derivedDistribution() //same for collation
Derive the distribution of the operator itelf from child operators.
4. MatchType distributionMatchType(int child) //same for collation
Returns the distribution match type for its nth child, how does it match the
other children.
Similar with Jinfeng's point, I think there should be 3 types of matching:
exact, satisfy, subset.
e.g.
R is distributed by (a), S is distributed by (a,b)
select * from R join S using a,b,c
If we have plan
HashJoin
|-- TableScan on R
+-- TableScan on S
We may require the match type on S to be satisfy. (a,b) satisfies required
distribution (a,b,c).
Fot the outer child R, we require it to be exact match with inner.
5. ExecOrder getExecOrder()
Returns how the operator's children is executed, left to right, or right to
left. Typically, hash join is right to left. We might use this as the
optimization order. To make sure we have correct plans, we have to optimize
child and enforce properties in the order that is specific to the physical
operator.
All the other dirty work should be done by the optimization engine, but not
through rules, I believe. However, I havn't got any clear plan on how to
achieve it inside the engine.
Haisheng
------------------------------------------------------------------
发件人：Jacques Nadeau<jacq...@apache.org>
日 期：2019年10月21日 11:04:19
收件人：<dev@calcite.apache.org>
主 题：Re: [DISCUSS] On-demand traitset request
Definitely agree that this has been a long time missing. I've been
challenged by this absence since before Calcite was Calcite. I also
remember the trials and tribulations around this that Jinfeng references
above.
In general, I think the first thing one might want to before actually doing
this is to make trait derivation internally defined based on the impact
that a rel node has on traits. I've always found the externally provided
rel traits to be problematic and a potential place for hidden bugs (row
type has the same problem) . It means that trait derivation of a relnode is
based on the rules that do transformation as opposed to the "physical"
impact of the relnode. (It also leads to derivation behavior for a relnode
being scattered in many different rules.) If moved to the rel node, it also
provides a second benefit, once you encapsulate this propagation logic, you
could also expose this as a trait derivation function that the planner
could use to seek out derivation paths.
At Dremio we toyed last year with the idea of adding a heuristic cycle on
top of the existing volano planner and relset state. In this model a
RelNode would have two additional methods: it would expose a trait
propagation function (as described above) and optionally expose one or more
specific traits this node desired. When the planner arrived at a
conclusion, you'd run the heuristic cycle to further propagate desired
traits (if possible) and then restart the planning cycle based on any new
transformations done during the heuristic stage. You'd then repeat this
volcano/trait prop cycle until you arrive at a "completed" state.
We never actually got to implementation but I'm super supportive of someone
picking this up.
On Sat, Oct 19, 2019 at 12:25 AM Stamatis Zampetakis <zabe...@gmail.com>
wrote:
> Thanks all for the very interesting usecases and helpful examples.
>
> I would like to stay a bit on the fact that logical operators do not have
> physical traits. Calcite's logical operators do have at least one physical
> trait which is Convention.NONE. Other logical operators such as:
>
> LogicalTableScan [1]
> LogicalFilter [2]
> LogicalProject [3]
> LogicalWindow [4]
>
> have additional traits regarding collation and distribution. There is
> already some sort of trait derivation so to some extend it is possible to
> check the traitset of the child (logical) operator before requesting some
> other traitset when creating the parent (physical).
>
> I see that this mechanism of adding explicitly traits to logical operators
> may be confusing and may also lead to planning problems. Replacing it by
> metadata might be a good idea and it is closer to the idea of
> "applicability function" mentioned in the Volcano paper. Assuming that we
> follow this approach I would assume that the traitset of logical operators
> from now on should be always empty.
>
> Is this what you have in mind Haisheng?
>
> Best,
> Stamatis
>
> [1]
>
> https://github.com/apache/calcite/blob/cd24cae77072e56e4333d10114bf380be79709f1/core/src/main/java/org/apache/calcite/rel/logical/LogicalTableScan.java#L95
> [2]
>
> https://github.com/apache/calcite/blob/cd24cae77072e56e4333d10114bf380be79709f1/core/src/main/java/org/apache/calcite/rel/logical/LogicalFilter.java#L105
> [3]
>
> https://github.com/apache/calcite/blob/cd24cae77072e56e4333d10114bf380be79709f1/core/src/main/java/org/apache/calcite/rel/logical/LogicalProject.java#L104
> [4]
>
> https://github.com/apache/calcite/blob/cd24cae77072e56e4333d10114bf380be79709f1/core/src/main/java/org/apache/calcite/rel/logical/LogicalWindow.java#L95
>
> On Sat, Oct 19, 2019 at 7:39 AM Xiening Dai <xndai....@gmail.com> wrote:
>
> > Thanks for the sharing. I like the way you model this problem, Jinfeng.
> >
> > There’s one minor issue with your example. Let say if R and S doesn’t
> have
> > sorting properties at all. In your case, we would end up adding enforcers
> > for LHS and RHS to get collation (a, b, c). Then we would need another
> > enforcer to get collation (b, c). This is a sub optimal plan as we could
> > have use (b, c, a) for join.
> >
> > I think in step #2, the join operator would need to take the agg trait
> > requirement into account. Then it would have two options -
> >
> > 1) require *exact/super* match of (b, c, a) or (c, b, a); this is to
> > guarantee the join output would deliver the collation agg needs.
> > 2) require permutation match of (a, b, c); in such case, an enforcer
> might
> > be needed for aggregation.
> >
> > Eventually the cost model decides who is the winner.
> >
> > There’s a fundamental difference between your model and Haisheng’s
> > proposal. In Haisheng’s case, a rel node not only looks at its parent’s
> > requirement, but also tries to get the potential traits its input could
> > deliver. It would try to align them to eliminate unnecessary
> alternatives.
> >
> > In above example, assuming R is (b, c, a) and S is (a, b, c), to
> implement
> > option 1), we would generate two alternatives -
> >
> > MergeJoin (b, c, a)
> > TableScan R
> > Sort(b, c, a)
> > TableScan S
> >
> > MergeJoin(c, b, a)
> > Sort(c, b, a)
> > TableScan R
> > Sort(c, b, a)
> > TableScan S
> >
> > But if we look at the input traits and has the insight that R already
> > delivers (b, c, a), we could decide to require (b, c, a) only and avoid
> > generating the 2nd plan, which is definitely worse, and reduce the search
> > space.
> >
> >
> > > On Oct 18, 2019, at 4:57 PM, Jinfeng Ni <j...@apache.org> wrote:
> > >
> > > A little bit of history. In Drill, when we first implemented
> > > Distribution trait's definition, we allows both exact match and
> > > partial match in satisfy() method. This works fine for single-input
> > > operator such aggregation, however it leads to incorrect plan for join
> > > query, i.e LHS shuffle with (a, b), RHS shuffle with (a) . At that
> > > time, we removed partial match, and use exact match only. Yet this
> > > changes leads to unnecessary additional exchange. To mitigate this
> > > problem, in join physical operator, for a join key (a, b, c), we
> > > enumerate different distribution requests, yet this lead to more space
> > > to explore and significantly increase planning time (which is probably
> > > what Haisheng also experienced). When I look back, I feel probably
> > > what we miss is the "coordination" step in the join operator, because
> > > if we relax the requirement of satisfy(), for multi-input operators,
> > > we have to enforce some "coordination", to make sure multiple input's
> > > trait could work together properly.
> > >
> > >
> > >
> > > On Fri, Oct 18, 2019 at 4:38 PM Jinfeng Ni <j...@apache.org> wrote:
> > >>
> > >> This is an interesting topic. Thanks for bringing up this issue.
> > >>
> > >> My understanding of Volcano planner is it works in a top-down search
> > >> mode (the parent asks for certain trait of its child), while the trait
> > >> propagates in a bottom-up way, as Stamatis explained.
> > >>
> > >> IMHO, the issue comes down to the definition of RelTrait, how to
> > >> determine if a trait A could satisfy a request asking for trait B,
> > >> that is, how RelTrait.satisfies() method is implemented.
> > >>
> > >> Let's first clarify different situations, using collation as example.
> > >> 1) The collation is requested by query's outmost ORDER BY clause.
> > >> - The generated plan has to have "exact match", i.e same collation
> > >> (same column sequence), or "super match" .
> > >> exact match: (a, b) satisfy (a, b)
> > >> super match: (a, b, c) satisfy (a, b)
> > >>
> > >> 2) The collation is requested by operand with single input, such as
> > >> sort-based Aggregation.
> > >> - In such case, a "permutation match" is sufficient.
> > >> For instance, for Aggregation (b,c), input with collation (c, b)
> > >> could satisfy the requirement.
> > >> permutation match: (b, c) satisfy (c, b). (c, b) satisfy (c,
> b)
> > >> permutation match: (b, c, a) satisfy (c, b). (c, b, a) satisfy
> (c,
> > b)
> > >>
> > >> 3) The collation is requested by operand with >= 2 inputs, such as
> > >> sort-based MergeJoin.
> > >> - A permutation match is sufficient for each input
> > >> - MergeJoin has to do coordination, after input's trait propagates
> > >> upwards. In other words, ensure both inputs's permutation match are
> > >> actually same sequence. Otherwise, enforcer could be inserted upon
> > >> each input, and the planner generates two plans and let the cost
> > >> decide.
> > >>
> > >> For the first case, this is how today's RelCollation's satisfy()
> > >> method is implemented.
> > >>
> > >> For the second / third cases, use Haisheng's example,
> > >>
> > >> SELECT DISTINCT c, b FROM
> > >> ( SELECT R.c c, S.b b FROM R, S
> > >> WHERE R.a=S.a and R.b=S.b and R.c=S.c) t;
> > >>
> > >> Aggregate . (c, b)
> > >> +--- MergeJoin . (a, b, c)
> > >> |--- TableScan on R
> > >> +--- TableScan on S
> > >>
> > >> Here is the steps that might take place in the planner:
> > >>
> > >> 1) Aggregate request permutation match collation (c, b)
> > >> 2) MergeJoin request a permutation match of (a, b,c) on both it's
> input
> > >> 3) R respond with collation (c, b, a), which satisfy MergeJoin's LHS
> > requirement
> > >> 4) S respond with collation (b, c, a), which satisfy MergeJoins' RHS
> > requirement
> > >> 5) MergeJoin do a coordination o LHS, RHS, and generate two possible
> > plans
> > >> MJ1: Insert a sort of (c, b, a) on RHS. This MJ operator now has
> > >> collation of (c, b, a)
> > >> MJ2: Insert a sort of (b, c, a) on LHS. This MJ operator now has
> > >> collation of (b, c, a)
> > >> 6) MJ1 and MJ2 could both satisfy permutation match request in step
> > >> 1, leading to two possible plans:
> > >> Agg1: with input of MJ1
> > >> Agg2: with input of MJ2
> > >> 7) planner chooses a best plan based on cost of Agg1 and Agg2.
> > >>
> > >> I should point that the enforcer sort inserted in step 5 could help
> > >> remove redundant sort in its input, if the input's collation is
> > >> obtained from sort, by invoking Calcite's SortRemove Rule.
> > >>
> > >> The above only considers the column sequence. The DESC/ASC, NULL
> > >> FIRST/LAST will add more complexity, but we probably use similar idea.
> > >>
> > >> In summary, we need :
> > >> 1) redefine collation trait's satisfy() policy, exact match, super
> > >> match, permutation match,
> > >> 2) different physical operator applies different trait matching
> > >> policy, depending on operator's # of inputs, and algorithm
> > >> implementation.
> > >>
> > >>
> > >>
> > >>
> > >>
> > >> On Fri, Oct 18, 2019 at 2:51 PM Haisheng Yuan <h.y...@alibaba-inc.com
> >
> > wrote:
> > >>>
> > >>> Hi Stamatis,
> > >>>
> > >>> Thanks for your comment. I think my example didn't make it clear.
> > >>>
> > >>> When a logical operator is created, it doesn't have any physical,
> > >>> propertyand it shouldn't have. When a physical operator is created,
> > >>> e.g. in Enumerable convention, it only creates an intuitive traitset
> > >>> with it, and requests it children the corresponding ones.
> > >>>
> > >>> For operators such as Join, Aggregate, Window, which may deliver
> > >>> multiple different traitsets, when the parent operator is created and
> > >>> request its traitset, it might be good to know what are the poosible
> > >>> traitset that the child operator can deliver. e.g.
> > >>>
> > >>> SELECT DISTINCT c, b FROM
> > >>> ( SELECT R.c c, S.b b FROM R, S
> > >>> WHERE R.a=S.a and R.b=S.b and R.c=S.c) t;
> > >>>
> > >>> Suppose R is ordered by (c, b, a), and S is ordered by (b, c, a).
> > >>> Here is the logical plan:
> > >>> Aggregate
> > >>> +--- InnerJoin
> > >>> |--- TableScan on R
> > >>> +--- TableScan on S
> > >>>
> > >>> When we create a physical merge join for the inner join, it may just
> > >>> have collation sorted on a,b,c. Then the aggreate on top of join will
> > >>> request another sort on c,b, thus we miss the best plan. What we
> > >>> can do is requesting all the order combinations, which is n!, like
> > >>> how the Values operator does. But that is too much.
> > >>>
> > >>> If we can provide an approach that can minimize the possiple traitset
> > >>> that the child operator may deliver, we can reduce the chance of
> > missing
> > >>> good plans. For the above query, the Aggregate operator can derive
> > >>> possible traitsets that its child operator join can deliver, in which
> > case,
> > >>> the possiple traitsets of join is
> > >>> 1. collation on (a,b,c) based on join condition,
> > >>> 2. collation on (c,b,a) based on left child,
> > >>> 3. collation on (b,c,a) based on right child
> > >>> So we can request Aggregate sorted by (c,b) and Join sorted by
> (c,b,a).
> > >>> The number of traiset requests and plan alternatives can be reduced.
> > >>> The DerivedTraitSets can be used to derive the possible traitsets
> from
> > >>> Join, and pass through Project, Filter etc...
> > >>>
> > >>> This is just an example of non-distributed system, for distributed
> > system,
> > >>> it can save much more by considering the possible distribution
> > delivered
> > >>> by child operators.
> > >>>
> > >>> One thing that concerns me is it highly relies on the traiset system
> > of the
> > >>> underlying physical system. Like Enumerable doesn't consider
> > distribution,
> > >>> because it is single-node system, but Hive/Flink are distributed
> > system.
> > >>> - Haisheng
> > >>>
> > >>> ------------------------------------------------------------------
> > >>> 发件人：Stamatis Zampetakis<zabe...@gmail.com>
> > >>> 日 期：2019年10月18日 14:53:41
> > >>> 收件人：<dev@calcite.apache.org>
> > >>> 主 题：Re: [DISCUSS] On-demand traitset request
> > >>>
> > >>> Hi Haisheng,
> > >>>
> > >>> This is an interesting topic but somehow in my mind I thought that
> this
> > >>> mechanism is already in place.
> > >>>
> > >>> When an operator (logical or physical) is created its traitset is
> > >>> determined in bottom-up fashion using the create
> > >>> static factory method present in almost all operators. In my mind
> this
> > is
> > >>> in some sense the applicability function
> > >>> mentioned in [1].
> > >>>
> > >>> Now during optimization we proceed in top-down manner and we request
> > >>> certain traitsets from the operators.
> > >>> If it happens and they contain already the requested traits nothing
> > needs
> > >>> to be done.
> > >>>
> > >>> In your example when we are about to create the sort-merge join we
> can
> > >>> check what traitsets are present in the inputs
> > >>> and if possible request those. Can you elaborate a bit more why do we
> > need
> > >>> a new type of metadata?
> > >>>
> > >>> Anyway if we cannot do it at the moment it makes sense to complete
> the
> > >>> missing bits since what you are describing
> > >>> was already mentioned in the original design of the Volcano optimizer
> > [1].
> > >>>
> > >>> "If a move to be pursued is the exploration of a normal query
> > processing
> > >>> algorithm such as merge-join, its cost is calculated by the
> algorithm's
> > >>> cost function. The algorithm's applicability function determines the
> > >>> physical properly vectors for the algorithms inputs, and their costs
> > and
> > >>> optimal plans are found by invoking FindBestPlan for the inputs. For
> > some
> > >>> binary operators, the actual physical properties of the inputs are
> not
> > as
> > >>> important as the consistency of physical properties among the inputs.
> > For
> > >>> example, for a sort-based implementation of intersection, i.e., an
> > >>> algorithm very similar to merge-join, any sort order of the two
> inputs
> > will
> > >>> suffice as long as the two inputs are sorted in the same way.
> > Similarly,
> > >>> for a parallel join, any partitioning of join inputs across multiple
> > >>> processing nodes is acceptable if both inputs are partitioned using
> > >>> Compatible partitioning rules. For these cases, the search engine
> > permits
> > >>> the optimizer implementor to specify a number of physical property
> > vectors
> > >>> to be tried. For example, for the intersection of two inputs R and S
> > with
> > >>> attributes A, B, and C where R is sorted on (A,B,C) and S is sorted
> on
> > >>> (B,A,C), both these sort orders can be specified by the optimizer
> > >>> implementor and will be optimized by the generated optimizer, while
> > other
> > >>> possible sort orders, e.g., (C,B,A), will be ignored. " [1]
> > >>>
> > >>> Best,
> > >>> Stamatis
> > >>>
> > >>> [1]
> > >>>
> >
> https://www.cse.iitb.ac.in/infolab/Data/Courses/CS632/Papers/Volcano-graefe.pdf
> > >>>
> > >>> On Fri, Oct 18, 2019 at 4:56 AM Haisheng Yuan <
> h.y...@alibaba-inc.com>
> > >>> wrote:
> > >>>
> > >>>> TL;DR
> > >>>> Both top-down physical TraitSet request and bottom-up TraitSet
> > >>>> derivation have their strongth and weakness, we propose
> > >>>> on-demand TraitSet request to combine the above two, to reduce
> > >>>> the number of plan alternatives that are genereated, especially
> > >>>> in distributed system.
> > >>>>
> > >>>> e.g.
> > >>>> select * from foo join bar on f1=b1 and f2=b2 and f3=b3;
> > >>>>
> > >>>> In non-distributed system, we can generate a sort merge join,
> > >>>> requesting foo sorted by f1,f2,f3 and bar sorted by b1,b2,b3.
> > >>>> But if foo happens to be sorted by f3,f2,f1, we may miss the
> > >>>> chance of making use of the delivered ordering of foo. Because
> > >>>> if we require bar to be sorted by b3,b2,b1, we don't need to
> > >>>> sort on foo anymore. There are so many choices, n!, not even
> > >>>> considering asc/desc and null direction. We can't request all
> > >>>> the possible traitsets in top-down way, and can't derive all the
> > >>>> possible traitsets in bottom-up way either.
> > >>>>
> > >>>> We propose on-demand traitset request by adding a new type
> > >>>> of metadata DerivedTraitSets into the built-in metadata system.
> > >>>>
> > >>>> List<RelTraitSet> deriveTraitSets(RelNode, RelMetadataQuery)
> > >>>>
> > >>>> In this metadata, every operator returns several possbile traitsets
> > >>>> that may be derived from this operator.
> > >>>>
> > >>>> Using above query as an example, the tablescan on foo should
> > >>>> return traiset with collation on f3, f2, f1.
> > >>>>
> > >>>> In physical implementation rules, e.g. the SortMergeJoinRule,
> > >>>> it gets possible traitsets from both child operators, uses the join
> > >>>> keys to eliminate useless traitsets, leaves out usefull traitsets,
> > >>>> and requests corresponding traitset on the other child.
> > >>>>
> > >>>> This relies on the feature of AbstractConverter, which is turned
> > >>>> off by default, due to performance issue [1].
> > >>>>
> > >>>> Thoughts?
> > >>>>
> > >>>> [1] https://issues.apache.org/jira/browse/CALCITE-2970
> > >>>>
> > >>>> Haisheng
> > >>>>
> > >>>>
> > >>>
> >
> >
>
