| From: | Venkat Balaji <venkat(dot)balaji(at)verse(dot)in> |
|---|---|
| To: | Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov> |
| Cc: | PGSQL Performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: : Cost calculation for EXPLAIN output |
| Date: | 2012-02-26 17:14:51 |
| Message-ID: | CAFrxt0jaSQ7ccfX9Oa_N7OPnXaNtaoQ9SEHgPDf3ZFgUEutbNQ@mail.gmail.com |
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| Lists: | pgsql-performance |
>
> > 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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