Re: : Cost calculation for EXPLAIN output

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От Venkat Balaji
Тема Re: : Cost calculation for EXPLAIN output
Дата
Msg-id CAFrxt0jaSQ7ccfX9Oa_N7OPnXaNtaoQ9SEHgPDf3ZFgUEutbNQ@mail.gmail.com
обсуждение исходный текст
Ответ на Re: : Cost calculation for EXPLAIN output  ("Kevin Grittner" <Kevin.Grittner@wicourts.gov>)
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> The cost is "13.88" to fetch 1 row by scanning an Primary Key
> indexed column.
>
> Isn't the cost for fetching 1 row is too high ?

I don't know, how many index pages will need to be randomly accessed
in addition to the random heap access?  How many dead versions of
the row will need to be visited besides the row which is actually
visible?  How many of these pages are in shared_buffers?  How many
of these pages are in OS cache?

Total Index pages are 140310. Yes. I suspect most of the times the required page is found in either OS cache or disk (shared_buffers is .9 GB) as we have 200+ GB of highly active database and the Index is on a 10GB table.

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