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https://issues.apache.org/jira/browse/TAJO-906?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14106747#comment-14106747
]
ASF GitHub Bot commented on TAJO-906:
-------------------------------------
Github user hyunsik commented on the pull request:
https://github.com/apache/tajo/pull/113#issuecomment-53052194
I've updated the patch. I've improved TajoTestingCluster to take system
properties as follows:
```
mvn clean install -DCODEGEN=true
```
If ```CODEGEN``` is a session variable, it will be applied to QueryContext
instance used in all unit tests. So, in order to test the code generation
feature, you should give ```-DCODEGEN=true``` when you execute ```mvn
install```. It can be used for other session variables too.
For test for real queries, you need to set a session variable CODEGEN as
follows:
```
tajo> \set CODEGEN true
tajo>
tajo> SELECT .....
```
> Runtime code generation for evaluating expression trees
> -------------------------------------------------------
>
> Key: TAJO-906
> URL: https://issues.apache.org/jira/browse/TAJO-906
> Project: Tajo
> Issue Type: Improvement
> Components: physical operator
> Reporter: Hyunsik Choi
> Assignee: Hyunsik Choi
> Fix For: 0.9.0
>
>
> We have used EvalNode for two purposes:
> * logical planning of expressions
> * evaluation of expressions
> EvalNode still is very nice for the purpose of logical planning. But, each
> EvalNode tree takes Datum included in a tuple and results in a Datum as a
> evaluation result.
> So, the current approach requires many object creations, and causes interpret
> overheads, meaning that each one evaluation involves tree traverses and many
> function calls. interpretation involves also many branches, and it is harmful
> to CPU pipelining.
> I propose Java byte code generation for each expression, and I'll use ASM
> (http://asm.ow2.org/) for it. This approach will write native java byte code,
> eliminating many condition branches and function calls. In addition, it is
> easier to deal with java primitive data types for expressions.
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