pgsql: doc: Mention possible ephemeral discrepancies in pg_stat_activit

doc: Mention possible ephemeral discrepancies in pg_stat_activity

Ephemeral inconsistencies across multiple attributes of pg_stat_activity
can exist as the system is designed to be efficient with a low overhead.
This question is raised by users from time to time based on the data
read in the view, so let's add a note in the docs about this
possibility.

Author: Alex Friedman <alexf01(at)gmail(dot)com>
Reviewed-by: Sami Imseih <samimseih(at)gmail(dot)com>
Discussion: https://postgr.es/m/8a275154-a654-44b0-ab37-197802f04c7b@gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f056f75dafd0025d26efaca026a87f14c079a130

Modified Files
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doc/src/sgml/monitoring.sgml | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)