There is now a PR: https://github.com/apache/calcite/pull/2024. Can
people please review?
Here's the TL;DR:
Previously, it was not easy to customize, re-use or extend planner
rules. If you wished to customize a rule (i.e. create a new instance
of a rule with different properties) you would have to call the rule's
constructor. Frequently the required constructor did not exist, so we
would have to add a new constructor and deprecate the old one.
After this change, you start off from an instance of the rule, modify
its configuration, and call toRule() on the configuration. (Rule
constructors are now private, because only the configuration ever
calls them.)
A good illustration of this is DruidRules, which used to contain many
sub-classes. Those sub-classes are no longer needed. Old code:
public static final DruidSortProjectTransposeRule SORT_PROJECT_TRANSPOSE =
new DruidSortProjectTransposeRule(RelFactories.LOGICAL_BUILDER);
public static class DruidSortProjectTransposeRule
extends SortProjectTransposeRule {
public DruidSortProjectTransposeRule(RelBuilderFactory
relBuilderFactory) {
super(
operand(Sort.class,
operand(Project.class, operand(DruidQuery.class, none()))),
relBuilderFactory, null);
}
}
New code:
public static final SortProjectTransposeRule SORT_PROJECT_TRANSPOSE =
SortProjectTransposeRule.INSTANCE.config
.withOperandFor(Sort.class, Project.class, DruidQuery.class)
.toRule();
The change maintains backwards compatibility to a large degree. In a
few places, I had to change rule instances from type RelOptRule to
Supplier<RelOptRule>, to avoid deadlocks during class loading. For
instance, instead of writing FilterJoinRule.FILTER_ON_JOIN you must
now write FilterJoinRule.FILTER_ON_JOIN.get().
Julian
On Thu, Apr 16, 2020 at 12:08 PM Julian Hyde <jh...@apache.org> wrote:
>
> I have now pushed a dev branch with a prototype. Please see
> https://issues.apache.org/jira/browse/CALCITE-3923 for details.
>
> Having built the prototype, I believe that this change is beneficial
> and we should do it. But I would like to get to consensus on the
> design before we pull the trigger.
>
> Julian
>
> On Tue, Apr 14, 2020 at 2:06 PM Julian Hyde <jh...@apache.org> wrote:
> >
> > Haisheng,
> >
> > I hear you. I agree that major changes to rules will require new rule
> > classes (not merely sub-classes). People should copy-paste, refactor,
> > and all that good stuff. But I think there are a lot of cases where we
> > need to make minor changes to rules (there are many of these in the
> > code base already), and this change will help.
> >
> > I have logged https://issues.apache.org/jira/browse/CALCITE-3923 and
> > am going to start working on a prototype. When we have a prototype we
> > will be able to assess how big an impact the API change will have.
> > (E.g. whether it will be a breaking change.)
> >
> > Julian
> >
> > On Sat, Mar 14, 2020 at 8:22 PM Haisheng Yuan <h.y...@alibaba-inc.com>
> > wrote:
> > >
> > > I don't think it is worth the refactoring. People who want to customize
> > > the rule, in most cases, won't be satisfied by a different parameter,
> > > they most likely still need to rewrite (copy & paste) the rule with some
> > > slightly their own logic. For many Calcite users, the rule is not
> > > reusable even with flexible configurations.
> > >
> > > - Haisheng
> > >
> > > ------------------------------------------------------------------
> > > 发件人：Stamatis Zampetakis<zabe...@gmail.com>
> > > 日 期：2020年03月14日 22:54:04
> > > 收件人：<dev@calcite.apache.org>
> > > 主 题：Re: [DISCUSS] Refactor how planner rules are parameterized
> > >
> > > Hello,
> > >
> > > Apologies for the late reply but I just realised that I had written the
> > > mail and never pressed the send button.
> > >
> > > I think it is a nice idea and certainly a problem worth addressing. If I
> > > understood well you're thinking something like the current constructor of
> > > the RelBuilder [1] that accepts a Context parameter. Indeed it seems that
> > > with this change even rules that are not designed to be configured can be
> > > changed much more gracefully (without adding new constructors and breaking
> > > changes).
> > >
> > > On the other hand, some of the advantages that you mention can also be
> > > turned into disadvantages. For instance, copying a rule without knowing
> > > the
> > > values of the other parameters is a bit risky and might be harder to
> > > reason
> > > about its correctness. Moreover, private constructors, final classes,
> > > etc.,
> > > are primarily used for encapsulation purposes so allowing the state of the
> > > rule escape somehow breaks the original design of the rule.
> > >
> > > Another problem with respect to rules is cross convention matching and
> > > transformations [2]. Many rules should not fire for operands that are in
> > > different conventions; a typical example that comes in my mind is
> > > FilterProjectTransposeRule [3]. In the same spirit most rules should not
> > > generate mixed convention transformations. Although a different problem, I
> > > am mentioning it here since it could affect the design of the new API.
> > >
> > > Best,
> > > Stamatis
> > >
> > > [1]
> > > https://github.com/apache/calcite/blob/f11115a2fe9e360f38910f112288581040e0ced5/core/src/main/java/org/apache/calcite/tools/RelBuilder.java#L155
> > >
> > > [2]
> > > https://lists.apache.org/thread.html/da1860f99f8bfd6ec7d26626c428ce1c55480e7c61ae7f83060a40c2%40%3Cdev.calcite.apache.org%3E
> > > [3]
> > > https://github.com/apache/calcite/blob/7c27b147414c64505fa33c947100ece094caa15c/core/src/main/java/org/apache/calcite/rel/rules/FilterProjectTransposeRule.java#L57
> > >
> > > On Thu, Feb 20, 2020 at 9:20 PM Michael Mior <mm...@apache.org> wrote:
> > >
> > > > This sounds reasonable to me. It also sounds like we could make this
> > > > backwards compatible by retaining (but deprecating) the existing
> > > > constructors and factory methods that will no longer be needed.
> > > > --
> > > > Michael Mior
> > > > mm...@apache.org
> > > >
> > > > Le jeu. 20 févr. 2020 à 13:11, Julian Hyde <jh...@apache.org> a écrit :
> > > > >
> > > > > I have an idea for a refactoring to RelOptRule. I haven’t fully
> > > > > thought
> > > > it through, but I’m going to sketch it out here to see whether folks
> > > > agree
> > > > about the problems/solutions.
> > > > >
> > > > > It will be a breaking change (in the sense that people will have to
> > > > change their code in order to get it to compile) but relatively safe (in
> > > > that once the code compiles, it will have the same behavior as before).
> > > > Also it will give Calcite developers and users a lot more flexibility
> > > > going
> > > > forward.
> > > > >
> > > > > The problem I see is that people often want different variants of
> > > > planner rules. An example is FilterJoinRule, which has a 'boolean smart’
> > > > parameter, a predicate (which returns whether to pull up filter
> > > > conditions), operands (which determine the precise sub-classes of
> > > > RelNode
> > > > that the rule should match) and a relBuilderFactory (which controls the
> > > > type of RelNode created by this rule).
> > > > >
> > > > > Suppose you have an instance of FilterJoinRule and you want to change
> > > > ‘smart’ from true to false. The ‘smart’ parameter is immutable (good!)
> > > > but
> > > > you can’t easily create a clone of the rule because you don’t know the
> > > > values of the other parameters. Your instance might even be
> > > > (unbeknownst to
> > > > you) a sub-class with extra parameters and a private constructor.
> > > > >
> > > > > So, my proposal is to put all of the config information of a
> > > > > RelOptRule
> > > > into a single ‘config’ parameter that contains all relevant properties.
> > > > Each sub-class of RelOptRule would have one constructor with just a
> > > > ‘config’ parameter. Each config knows which sub-class of RelOptRule to
> > > > create. Therefore it is easy to copy a config, change one or more
> > > > properties, and create a new rule instance.
> > > > >
> > > > > Adding a property to a rule’s config does not require us to add or
> > > > deprecate any constructors.
> > > > >
> > > > > The operands are part of the config, so if you have a rule that
> > > > > matches
> > > > a EnumerableFilter on an EnumerableJoin and you want to make it match an
> > > > EnumerableFilter on an EnumerableNestedLoopJoin, you can easily create
> > > > one
> > > > with one changed operand.
> > > > >
> > > > > The config is immutable and self-describing, so we can use it to
> > > > automatically generate a unique description for each rule instance.
> > > > >
> > > > > Julian
> > > > >
> > > > > [1]
> > > > https://github.com/apache/calcite/blob/5fa41609cb0fe310a0a11d86319d861423850a36/core/src/main/java/org/apache/calcite/rel/rules/FilterJoinRule.java#L93
> > > > <
> > > > https://github.com/apache/calcite/blob/5fa41609cb0fe310a0a11d86319d861423850a36/core/src/main/java/org/apache/calcite/rel/rules/FilterJoinRule.java#L93
> > > > >
> > > > >
> > > >
> > >
