​But how can I handle the unexpected variation of the input class type ?
For example, please consider the following *RelOptRule* constructor​
public IncortaLimitRule() {
> super(operand(*DrillLimitRel*.class, operand(*IncortaJdbcDrel*.class,
> operand(*JdbcRel*.class, any()))), "TestRule");
> }
I'm trying to be precise so I specified the RelNode (*DrillLimitRel*), it's
input (*IncortaJdbcDrel*) and it's input's input (*JdbcRel*, this is an
interface but I understand that the planner should match relnodes if the
rule's operand is a parent of examined operand, so for instance,
*JdbcTableScan* should match).
Is there a way to guarantee the relnode's input type ? Looking into other
rules, I don't remember seeing type checking for input relnodes. Is it a
good sign that I have to do multiple checks for the input relnode type ?
*---------------------*
*Muhammad Gelbana*
On Tue, Jun 27, 2017 at 1:36 AM, Julian Hyde <jh...@apache.org> wrote:
> RelSubset provides a level of indirection that allows Calcite to optimize
> queries. If the input to a relational operator is an equivalence class, not
> a particular relational expression, then Calcite has the freedom to choose
> the member of the equivalence class that has the cheapest cost.
>
> Calcite uses the Volcano algorithm, a form of dynamic programming, to do
> this.
>
> As you have discovered it means that you cannot simply tree-walk over a
> relational expression, looking for, say, a Project on top of a Filter. You
> need to write a RelOptRule that declares that it wants to see a Project on
> top of a Filter, and Volcano will fire that rule whenever that combination
> arises.
>
> Julian
>
>
> > On Jun 26, 2017, at 4:00 PM, Muhammad Gelbana <m.gelb...@gmail.com>
> wrote:
> >
> > While debugging through some of the rules I'm trying to get to work, I
> find
> > that the matched relnode's input is *HepRelVertex* or a *RelSubset*.
> >
> > Why wouldn't I be getting a descendant of the following types:
> >
> > - BiRel
> > - MultiJoin
> > - SetOp
> > - SingleRel
> > - TableScan
> >
> > There are other types too but I can assume how to handle the types I
> listed.
> >
> > *RelSubset* is really confusing because, as far as I understand, it's a
> > group of relnodes. So how can I decide which node to get from this group
> so
> > I can use it as an input to the new relnode I'm creating ?! Or should I
> > pass the *RelSubset* itself ? Why am I getting it in the first place and
> > not a single relnode ?
> >
> > *---------------------*
> > *Muhammad Gelbana*
>
>
