yes it is
show constraint_exclusion
partition
and if I explain the same query with an other filter
explain select * from wiki_data_part where category='fr'
| Append (cost=0.00..14010.76 rows=291609 width=48)
| -> Seq Scan on wiki_data_part_f (cost=0.00..9975.04 rows=291339
width=48)
| Filter: ((category)::text = 'fr'::text)
| -> Seq Scan on wiki_data_part_s (cost=0.00..4035.72 rows=270 width=50)
| Filter: ((category)::text = 'fr'::text)
wiki_data_part_s is always chosen in the plan
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Sent from: http://www.postgresql-archive.org/PostgreSQL-general-f1843780.html