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https://issues.apache.org/jira/browse/TAJO-838?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14260829#comment-14260829
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ASF GitHub Bot commented on TAJO-838:
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Github user jihoonson commented on the pull request:
https://github.com/apache/tajo/pull/231#issuecomment-68331921
@hyunsik, thanks for your comment.
Here are my answers.
1. On physical properties: When creating a BST index, the index keys are
sorted. The sort specifications in the ```CREATE INDEX``` statement are used to
specify the sort order of index keys. Maybe, we can use this feature for
performance boost of some other operations such as merge sort or sort-merge
join.
Since the sort specifications represent the sort order of index keys in a
newly created index, I think that users can specify their preferred sort
specifications which will be beneficial for future queries.
2. On the index maintenance issue: If a base table is changed, every index
created on that table must be updated. To handle this problem, we need to
introduce a new feature, such as the trigger of database systems. However,
since this will induce a huge amount of work, it would be better to proceed in
another issue. Until that, we may leave the index maintenance problem to users.
IMHO, since this feature is still experimental, it would be enough.
3. On showing index information: you can see information about the created
indexes when executing the ```\d [tablename]``` command. Of course, we need to
show more detailed information in future. I'll add this to our documentation,
too.
> 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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