Re: any way to use indexscan to get last X values - Mailing list pgsql-performance

From Tomaz Borstnar
Subject Re: any way to use indexscan to get last X values
Date
Msg-id 5.2.1.1.0.20030615171224.01c32eb0@127.0.0.1
Whole thread Raw
In response to Re: any way to use indexscan to get last X values with "order by Y limit X" clause?  ("Shridhar Daithankar" <shridhar_daithankar@persistent.co.in>)
List pgsql-performance
At 16:31 15.6.2003, Shridhar Daithankar wrote:

>Question. The field approved seems to have boolean values. If probability of
>having either of value is 50%, I doubt planner will use index anyway.

True. It has Y or N only so index on approved is useless. But using index
on ORDER BY part would help a lot since it knows to fetch last X ordered
values.

>Correct me if I am wrong.
Unfortunately you are very right.

I am not sure how to stuff modifystamp and thread into WHERE clause to make
it use indexes on thread and/or modifystamp. So far I believe this would be
the only way to use them, right?

Tomaz



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