| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Kevin Grittner <kgrittn(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Ants Aasma <ants(dot)aasma(at)eesti(dot)ee>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Kevin Grittner <kgrittn(at)postgresql(dot)org>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, "pgsql-committers(at)postgresql(dot)org" <pgsql-committers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Re: pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold < |
| Date: | 2016-06-16 17:44:34 |
| Message-ID: | CA+TgmobCZGouJU=z5e2HYDRNYhD24HpwOsS11K3YZUUyoX6Lwg@mail.gmail.com |
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On Thu, Jun 16, 2016 at 12:54 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> The root of my confusion is: if we prune a tuple, we'll bump the page
>> LSN, so any session that is still referencing that tuple will error
>> out as soon as it touches the page on which that tuple used to exist.
>
> Right. On the main table. But we don't peform that check on the toast
> table/pages. So if we prune toast tuples, which are still referenced by
> (unvacuumed) main relation, we can get into trouble.
OK, if it's true that we don't perform that check on the TOAST table,
then I agree there's a potential problem there. I don't immediately
know where in the code to look to check that.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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