Github user hyunsik commented on a diff in the pull request:
https://github.com/apache/tajo/pull/887#discussion_r46377850
--- Diff: tajo-docs/src/main/sphinx/index/how_to_use.rst ---
@@ -66,4 +67,10 @@ If you don't want to use the index scan feature anymore,
you can simply disable
.. note::
- Once the index scan feature is enabled, Tajo currently always
performs the index scan regardless of its efficiency. You should set this
option when the expected number of retrieved tuples is sufficiently small.
+ Once index scan is enabled, Tajo currently always performs index scan
regardless of its efficiency. You should set this option when the expected
number of retrieved tuples is sufficiently small.
--- End diff --
I suggest:
``Once index scan is enabled, Tajo will perform 'index scan' if possible.
In some cases, it may cause performance degradation. If you always want to get
better performance, you should either enable or disable 'index scan' according
to selectivity. Usually, the performance gain of index will increase when the
selectivity is low.``
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