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

On Mon, May 2, 2016 at 10:21 AM, Andres Freund <andres(at)anarazel(dot)de> 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.

You are certainly welcome to add a new open item to cover those
complaints. But I do not want to blur together the discussion of
whether the feature is well-designed with the question of whether it
regresses performance when it is turned off. Those are severable
issues, meriting separate discussion (and probably separate threads).

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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