| From: | Kevin Grittner <kgrittn(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>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Ants Aasma <ants(dot)aasma(at)eesti(dot)ee>, Kevin Grittner <kgrittn(at)postgresql(dot)org>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Re: [COMMITTERS] pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold < |
| Date: | 2016-07-13 15:06:52 |
| Message-ID: | CACjxUsNERjp3BBBWfgs4mg3CyA+O0ATN1=O4NM3MWC3_LHP-dg@mail.gmail.com |
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| Lists: | pgsql-committers pgsql-hackers |
On Wed, Jul 13, 2016 at 7:57 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Tue, Jul 12, 2016 at 8:34 PM, Kevin Grittner <kgrittn(at)gmail(dot)com> wrote:
>> On Fri, Jul 8, 2016 at 1:52 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>>
>>> I'm a bit confused, why aren't we simply adding LSN interlock
>>> checks for toast? Doesn't look that hard? Seems like a much more
>>> natural course of fixing this issue?
>>
>> I took some time trying to see what you have in mind, and I'm
>> really not "getting it".
>
> Isn't it possible if we initialize lsn and whenTaken in SnapshotToast
> when old_snapshot_threshold > 0 and add a check for
> HeapTupleSatisfiesToast in TestForOldSnapshot()?
With that approach, how will we know *not* to generate an error
when reading the chain of tuples for a value we are deleting. Or
positioning to modify an index on toast data. Etc., etc. etc.
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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