Обсуждение: old_snapshot_threshold documentation

I doubt the documentation for old_snapshot_threshold is going to be
understood by many ordinary users.  What is a "snapshot", first of all?
Why would a snapshot be old?  Why is that a problem?  What can I do to
avoid it?  What are the circumstances in practice where this issue would
arise, and what are the trade-offs?  Where can I see existing snapshots
and how old they are?

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

On Fri, Aug 26, 2016 at 1:34 PM, Peter Eisentraut
<peter.eisentraut@2ndquadrant.com> wrote:
> I doubt the documentation for old_snapshot_threshold is going to be
> understood by many ordinary users.  What is a "snapshot", first of all?
> Why would a snapshot be old?  Why is that a problem?  What can I do to
> avoid it?  What are the circumstances in practice where this issue would
> arise, and what are the trade-offs?  Where can I see existing snapshots
> and how old they are?

I'll put something together to improve that.  I think largely that
will consist of references to other sections of the documentation,
like MVCC, vacuuming, pg_stat_activity, etc.

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