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

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Kevin Grittner <kgrittn(at)gmail(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>, "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: 2016-05-03 05:24:38
Message-ID: 20160503052438.GA27541@momjian.us
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On Mon, May 2, 2016 at 07:21:21AM -0700, Andres Freund wrote:
> On 2016-05-02 09:03:19 -0400, Robert Haas wrote:
> > On Fri, Apr 29, 2016 at 6:08 PM, Kevin Grittner <kgrittn(at)gmail(dot)com> wrote:
> > > Now to continue with the performance benchmarks. I'm pretty sure
> > > we've fixed the problems when the feature is disabled
> > > (old_snapshot_threshold = -1), and there are several suggestions
> > > for improving performance while it is on that need to be compared
> > > and benchmarked.
> >
> > If anyone thinks that the issue with the feature disabled is NOT
> > fixed, please speak up! I'm moving the corresponding open item to
> > CLOSE_WAIT status, meaning that it will be closed if nobody shows up
> > to say that there is still an issue.
>
> Well, I don't agree that the feature is in a releaseable state. The
> datastructure is pretty much non-scalable, and maintained on the wrong
> side (every read, instead of once in writing writing xacts). There's no
> proposal actually addressing the scalability issues.

I also strongly question whether we should revert this feature and try
again in 9.7.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +

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