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https://issues.apache.org/jira/browse/PIG-1178?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12799859#action_12799859
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Ying He commented on PIG-1178:
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a couple questions on expression operators:
1. 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? 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.
2. 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
> 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.
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