Hyunsik Choi created TAJO-501:
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Summary: Rewrite thehe projection part of logical planning
Key: TAJO-501
URL: https://issues.apache.org/jira/browse/TAJO-501
Project: Tajo
Issue Type: Improvement
Components: planner/optimizer
Reporter: Hyunsik Choi
Assignee: Hyunsik Choi
Priority: Critical
Fix For: 0.8-incubating
The projection part of LogicalPlanner was designed long time ago. It has
evolved to support many SQL expressions. However, due to its rough design, it
is hard to be improved for further SQL expressions and it causes many bugs.
The current logical planner has the following problems:
* other expressions except for column can be used in group-by clause.
* TAJO-422
* other expressions except for column can not be used in order-by clause.
* An expression including some aggregation function must be evaluated in
group-by executor.
* As a result, some aggregation operator like HashAggregateExec has to keep
all intermediate results of a complex expression in a hash table.
* It also causes frequent GC and large memory consumption.
The too high code complexity also causes many bugs like
* TAJO-434 - java.lang.NullPointerException for invalid column name
* TAJO-428 - CASE WHEN IS NULL condition is a problem using LEFT OUTER JOIN
* TAJO-463 - ProjectionPushDownRule incorrectly rewrite the output schema of
StoreTableNode
* TAJO-443 - Order by query gives NullPointerException at at
org.apache.tajo.catalog.Schema.getColumnId(Schema.java:142)
The major reason of this problem is as follows:
* TargetListManager keeps only the final target list.
* SELECT col1, sum(col2) as col2, ... <- the final target list
* TargetListManager deals with each expression described in a target list or
other clauses like group-by clause as a singleton expression.
The main objective of this issue is to rewrite the projection part of logical
planning in order to those problems.
For 2 weeks, I've rewritten this part. I'll submit the patch soon.
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