| From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
|---|---|
| To: | Dmitriy Sarafannikov <dsarafannikov(at)yandex(dot)ru> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)anarazel(dot)de>, Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Borodin Vladimir <root(at)simply(dot)name>, Хомик Кирилл <khomikki(at)yandex-team(dot)ru> |
| Subject: | Re: [PROPOSAL] Use SnapshotAny in get_actual_variable_range |
| Date: | 2017-05-01 11:58:39 |
| Message-ID: | CAA4eK1+bG5rbp54iHy2xcrD85-asiMPG1MRF5+Xmk9rMGNGzXA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Apr 28, 2017 at 10:02 PM, Dmitriy Sarafannikov
<dsarafannikov(at)yandex(dot)ru> wrote:
>
> What I'm thinking of is the regular indexscan that's done internally
> by get_actual_variable_range, not whatever ends up getting chosen as
> the plan for the user query. I had supposed that that would kill
> dead index entries as it went, but maybe that's not happening for
> some reason.
>
>
> Really, this happens as you said. Index entries are marked as dead.
> But after this, backends spends cpu time on skip this killed entries
> in _bt_checkkeys :
>
If that is the case, then how would using SnapshotAny solve this
problem. We get the value from index first and then check its
visibility in heap, so if time is spent in _bt_checkkeys, why would
using a different kind of Snapshot solve the problem?
--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com
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