| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Noah Misch <noah(at)leadboat(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Ants Aasma <ants(dot)aasma(at)eesti(dot)ee>, Kevin Grittner <kgrittn(at)postgresql(dot)org>, Kevin Grittner <kgrittn(at)gmail(dot)com> |
| Subject: | Re: old_snapshot_threshold allows heap:toast disagreement |
| Date: | 2016-08-02 03:40:40 |
| Message-ID: | CA+TgmoY0UEEtFw9+9v3iLmUSAjtJPT0wpUk=zPcGr8mJ1QNz3g@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sat, Jul 30, 2016 at 8:17 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Fri, Jul 29, 2016 at 1:10 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Wed, Jul 27, 2016 at 7:26 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>>
>> New version attached.
>
> +static inline void
> +InitToastSnapshot(Snapshot snapshot, XLogRecPtr lsn)
> +{
> + snapshot->satisfies = HeapTupleSatisfiesToast;
> + snapshot->lsn = lsn;
> +}
>
> Here, don't you need to initialize whenTaken as that is also used in
> TestForOldSnapshot_impl() to report error "snapshot too old".
Hmm, yeah. This is actually a bit confusing. We want the "oldest"
snapshot, but there are three different notions of "oldest":
1. Smallest LSN.
2. Smallest whenTaken.
3. Smallest xmin.
Which one do we use?
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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