Re: Question about behavior of snapshot too old feature

On Mon, Oct 17, 2016 at 08:04:43AM -0500, Kevin Grittner wrote:
> > We have regression test for this feature but it sets
> > old_snapshot_threshold = 0, I doubt about we can test it properly.
> > Am I missing something?
>
> This is a hard feature to test properly, and certainly hard to test
> without the test running for a long time. The zero setting is
> really not intended to be used in production, but only to allow
> some half-way decent testing that doesn't take extreme lengths of
> time. If you add some delays of a few minutes each at key points
> in a test, you should be able to get a test that works with a
> setting of 1min. It is not impossible that we might need to add a
> memory barrier to one or two places to get such tests to behave
> consistently, but I have not been able to spot where, if anywhere,
> that would be.

Slide 10 of this presentation has an example showing
old_snapshot_threshold set to '1min':

http://momjian.us/main/writings/pgsql/features.pdf

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

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