| From: | Kevin Grittner <kgrittn(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Robert Haas <robertmhaas(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: | 2016-06-15 21:58:25 |
| Message-ID: | CACjxUsOQCDDGmhEXb0Bh74Nfxhy9gGYnwdKvpn=VK1fR_7UH3g@mail.gmail.com |
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| Lists: | pgsql-committers pgsql-hackers |
On Wed, Jun 15, 2016 at 3:25 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2016-06-15 14:24:58 -0500, Kevin Grittner wrote:
>> On Wed, Jun 15, 2016 at 2:20 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>>
>> > We might fetch a toast tuple which
>> > since have been re-purposed for a datum of a different type.
>>
>> How would that happen?
>
> Autovac vacuums toast and heap tables independently. Once a toast datum
> isn't used anymore, the oid used can be reused (because it doesn't
> conflict via GetNewOidWithIndex() anymore. If analyze then detoasts a
> datum, which hasn't been removed, the contents of that toast id, might
> actually be for something different.
What prevents that from happening now, without STO?
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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