Julian Hyde created CALCITE-3923:
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Summary: Refactor how planner rules are parameterized
Key: CALCITE-3923
URL: https://issues.apache.org/jira/browse/CALCITE-3923
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
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.
(See the email thread [[DISCUSS] Refactor how planner rules are
parameterized|https://lists.apache.org/thread.html/rfdf6f9b7821988bdd92b0377e3d293443a6376f4773c4c658c891cf9%40%3Cdev.calcite.apache.org%3E].)
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