Re: Re: [COMMITTERS] pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold <

From: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
To: Kevin Grittner <kgrittn(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 12:57:46
Message-ID: CAA4eK1+B4fu5haTGg1ajyuRF9EK2ZhJsgTu7cT1GDArPHqe+0w@mail.gmail.com
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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 Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com

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