| From: | "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com> |
|---|---|
| To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: HOT is applied |
| Date: | 2007-09-21 14:22:20 |
| Message-ID: | 2e78013d0709210722h55f8535dwd2a6941da7cc0d1b@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 9/21/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>
> so this example is getting past the heuristic tests in
> heap_page_prune_opt almost every time. Why is that? Too tired to poke
> at it more tonight.
>
>
I guess you already know the answer now, but anyways: Since we are
updating a single tuple in a single transaction, each update is preceded
by a sequential scan. All but last pages are completely full and marked
prunable, so HOT would try to (unsuccessfully) prune every (except may
be last) page.
Thanks,
Pavan
--
Pavan Deolasee
EnterpriseDB http://www.enterprisedb.com
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