| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Kevin Grittner <kgrittn(at)gmail(dot)com> |
| Cc: | 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>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, 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 17:47:17 |
| Message-ID: | 20160713174717.n6ncoopyxnatp5d7@alap3.anarazel.de |
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| Lists: | pgsql-committers pgsql-hackers |
On 2016-07-12 10:04:45 -0500, Kevin Grittner 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". I definitely applaud you for spotting the
> problem, but this suggestion for solving it doesn't seem to be
> useful.
...
> Basically, after turning this suggestion every way I could, I see
> two alternative ways to implement it.
What I was actually getting at was to perform TestForOldSnapshot() in
the HeapTupleSatisfiesToast case as well. That'd require minor amounts
of work to keep the lsn up2date, but otherwise should be fairly easy to
implement. It seems much more logical to use the same mechanism we use
for heap for toast as well, rather than implementing something separate.
- Andres
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