[
https://issues.apache.org/jira/browse/PIG-158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12584744#action_12584744
]
Alan Gates commented on PIG-158:
--------------------------------
I like Pi's idea of operator containing plans of operators in that it does fit
our nested model well. My concern is state in our visitors. Right now a
visitor contains a reference to the plan it is visiting because it must
traverse the plan. When the visitor comes to a node that contains a plan, how
does it then visit that plan? I don't want to have to spawn a new visitor,
because if there's information learned or state changed in that second visitor,
it has to somehow be transmitted back to the original visitor.
One possibility is to follow another suggestion that Pi gave, which is to
separate walkers and visitors. A walker would be associated with the plan. A
visitor would keep a stack of walkers. When it encountered a nested plan, it
would push its current walker on the stack, spawn a new walker with the nested
plan, and visit that nested plan. When it finished it could pop the previous
walker back off the stack and continue.
In this proposal visiting a filter operator would look something like this:
{code}
class LOVisitor {
visit(Filter f) {
Walker w = new Walker(f.getComparisonPlan());
walkers.push(currentWalker);
currentWalker = w;
f.getComparisonPlan().getRoot().visit(this);
currentWalker = walkers.pop();
}
}
{code}
This allows us to have nested plans, keep state across visitations of nested
plans, and not go through separating expression operators from logical
operators.
On the down side, it does make visitor logic a more complex. Anyone see any
other downsides?
> Rework logical plan
> -------------------
>
> Key: PIG-158
> URL: https://issues.apache.org/jira/browse/PIG-158
> Project: Pig
> Issue Type: Sub-task
> Components: impl
> Reporter: Alan Gates
> Assignee: Alan Gates
> Attachments: logical_operators.patch, logical_operators_rev_1.patch,
> logical_operators_rev_2.patch, logical_operators_rev_3.patch
>
>
> Rework the logical plan in line with
> http://wiki.apache.org/pig/PigExecutionModel
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
