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

On Wed, Apr 13, 2016 at 10:01 AM, Andres Freund <andres@anarazel.de> wrote:

> My problem with that is that snapshot-too-old is essentially a
> efficiency feature for busy and large databases. Regressing noticeably
> when it's enabled in it's natural habitat seems sad.

With a real-world application with realistic simulated user load
there was no such regression and a big gain in performance over
time, so we're talking about adjusting how broad a range of
workloads it benefits.  I don't have a strong opinion yet, since I
haven't run the benchmarks on big machines (scheduled for the day
after tomorrow); but as an example, if I only see such regression
on a Linux kernel with version a version < 3.8 I am going to be
less concerned about getting something into 9.6, since IMO it is
completely irresponsible to run a NUMA machine with 4 or more nodes
on an OS with a substandard NUMA scheduler.  I'm not sure when 3.8
became available, but according to Wikipedia Version 3.10 of the
Linux kernel was released in June 2013, so it's not like you need
to be on the bleeding edge to have a decent scheduler.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company