Re: How to see index was rejected for seq scan?

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От Corey Taylor
Тема Re: How to see index was rejected for seq scan?
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Msg-id CADBz386etzbEwYPx_WCDWHD=acbXSAb+qKFu6v79YhFj0qBJww@mail.gmail.com
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Ответ на Re: How to see index was rejected for seq scan?  (Peter Eisentraut <peter.eisentraut@2ndquadrant.com>)
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> But for simple queries, you might get some insight if you set
> enable_seqscan to off.  Then the planner will give you an index-using
> plan if it is at all possible.  Then you can compare the costs.  If the
> planner still gives you a sequential scan, then the index was not
> applicable for other reasons.

Thanks!  This gives me enough information. I was essentially looking for something concrete to discuss for cases where someone even more novice than myself in query optimization points to issues after adding an index.

I have a tangential question that I am curious about more than it being helpful in building queries.

Is index information used to determine the input scan cost or is that determine through another mechanism or other metadata in the table?  I mean this for a simple case and not in an exhaustive general sense.  For example a table with an id and timestamp column with an index on the id and timestamp filtered by a date range. 

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