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https://issues.apache.org/jira/browse/TAJO-838?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14260352#comment-14260352
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ASF GitHub Bot commented on TAJO-838:
-------------------------------------
Github user hyunsik commented on the pull request:
https://github.com/apache/tajo/pull/231#issuecomment-68293902
It's excellent. It's works very well. It's performance gain was larger than
I expected. I definitely think that this feature is very promising. Probably,
this feature may differentiate Tajo from other competitive systems.
The objective of following questions is to make this feature more solid and
more consistent.
While I'm testing features on a local cluster, I get some questions.
In some tests, CREATE INDEX statement includes physical properties as the
following example:
```
create index l_orderkey_idx on lineitem (l_orderkey asc null first);
```
How does a specified sort order affects index creation? I tested it with
```asc``` as well as ```desc```. But, it works well in both cases. Is it just a
hint?
In addition, such a physical property is fragile due to following reasons:
* It is hard for users to ensure the table properties.
* INSERT (OVERWRITE) INTO AS SELECT can change the physical properties.
How do you think about them? After I get your answer, I'll give additional
questions.
Also, I have feature wish.
* There is no way to show already created indexes and their information.
> Improve query planner to utilize index
> --------------------------------------
>
> Key: TAJO-838
> URL: https://issues.apache.org/jira/browse/TAJO-838
> Project: Tajo
> Issue Type: Sub-task
> Components: planner/optimizer
> Reporter: Jihoon Son
> Assignee: Jihoon Son
> Priority: Minor
>
> Index can improve the query performance when the selectivity of query is high.
> Thus, query planner should decide whether index is used or not for a given
> query.
> The selectivity can be guessed using statistics.
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