[
https://issues.apache.org/jira/browse/PIG-1178?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12800054#action_12800054
]
Alan Gates commented on PIG-1178:
---------------------------------
bq. in ProjectExpression, is it better to change the object variable "input"
from "int" to "LogicalRelationalOperator" to point to the operator that the
project expression operates on directly?
I want to avoid references to the actual relational operators in the
expressions because it makes patching up the plans after a transformation much
easier. If each project keeps a reference to the relational operator, then
when the plan is transformed we have to go to every project and change its
reference. By keeping pointers only to which input number, we don't have to
make any changes in the projects after a transformation in the plan.
bq. And I don't understand why this operator needs alias it references. But if
we change input to operator object, the alias can be get from the operator.
You're right, we shouldn't double store aliases here. We should just use the
uid and the project reference. I'll make the change.
bq. I don't know the purpose of ColumnExpression. Is it to capture operands? It
doesn't seem to have any special features. So I am not sure if it is necessary
It's a super class for all expressions that represent a single value:
projection, constants, and eventually, tuple and map dereferences. I think
it's useful for understanding the categorization of expressions. I'm not sure
it adds any functionality.
> LogicalPlan and Optimizer are too complex and hard to work with
> ---------------------------------------------------------------
>
> Key: PIG-1178
> URL: https://issues.apache.org/jira/browse/PIG-1178
> Project: Pig
> Issue Type: Improvement
> Reporter: Alan Gates
> Assignee: Ying He
> Attachments: expressions.patch, lp.patch, PIG_1178.patch
>
>
> The current implementation of the logical plan and the logical optimizer in
> Pig has proven to not be easily extensible. Developer feedback has indicated
> that adding new rules to the optimizer is quite burdensome. In addition, the
> logical plan has been an area of numerous bugs, many of which have been
> difficult to fix. Developers also feel that the logical plan is difficult to
> understand and maintain. The root cause for these issues is that a number of
> design decisions that were made as part of the 0.2 rewrite of the front end
> have now proven to be sub-optimal. The heart of this proposal is to revisit a
> number of those proposals and rebuild the logical plan with a simpler design
> that will make it much easier to maintain the logical plan as well as extend
> the logical optimizer.
> See http://wiki.apache.org/pig/PigLogicalPlanOptimizerRewrite for full
> details.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
