One Partition by list is always chosen by planner

Hello,

after creating a table wiki_data_part with
partition by list (category);

and creating partitions like
CREATE TABLE wiki_data_part_a PARTITION OF wiki_data_part
FOR VALUES IN ('ang.q',...,'arc');
CREATE TABLE wiki_data_part_b PARTITION OF wiki_data_part
FOR VALUES IN ('bs.s',...,'bg.n');

copy table wiki_data_part from ...;

analyze wiki_data_part;

explain select * from wiki_data_part where category='en'

| Append  (cost=0.00..21595.75 rows=4 width=102)
                                                                                 
 
|   ->  Seq Scan on wiki_data_part_e  (cost=0.00..21578.00 rows=1 width=102)
                                                                                 
 
|         Filter: ((category)::text = 'en'::text)
                                                                                 
 
|   ->  Seq Scan on wiki_data_part_s  (cost=0.00..17.75 rows=3 width=102)
                                                                                 
 
|         Filter: ((category)::text = 'en'::text)    

partition wiki_data_part_s (that has more than 100 values in its list) is
always scanned,
even when where predicates are not in its values list ...

Problem occurs on
PostgreSQL 10.0, compiled by Visual C++ build 1800, 64-bit
even without data loaded.

If this is a problem of max values, maybe this could be added in doc ?


wiki_data_wrong_part_s_chosen.sql
<http://www.postgresql-archive.org/file/t348768/wiki_data_wrong_part_s_chosen.sql>  



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