Bug #809: View not using index

Philip Warner (pjw(at)rhyme(dot)com(dot)au) reports a bug with a severity of 2
The lower the number the more severe it is.

Short Description
View not using index

Long Description
It seems that a UNION view fails to use underlying table indexes. This is a major pain when using subclassed tables which are updated frquently - even if the underlying tables are vacuumued regularly, the seq scan can take a very long time.

Sample Code

create table t1(id serial,name text);
insert into t1(name) values('fred');
insert into t1(name) select name || id from t1;
insert into t1(name) select name || id from t1;
...keep doing this until the table is big

create table t2(id serial,name text);

create view tv as select id,name from t1 union select id,name from t2;

vacuum full;
analyze;

explain select * from t1 where id=1;
NOTICE: QUERY PLAN:

Index Scan using t1_id_key on t1 (cost=0.00..3.01 rows=1 width=34)

explain select * from tv where id=1;

NOTICE: QUERY PLAN:

Subquery Scan tv (cost=24029.48..24821.48 rows=15840 width=36)
-> Unique (cost=24029.48..24821.48 rows=15840 width=36)
-> Sort (cost=24029.48..24029.48 rows=158401 width=36)
-> Append (cost=0.00..2739.00 rows=158401 width=36)
-> Subquery Scan *SELECT* 1 (cost=0.00..2739.00 rows=158400 width=34)
-> Seq Scan on t1 (cost=0.00..2739.00 rows=158400 width=34)
-> Subquery Scan *SELECT* 2 (cost=0.00..0.00 rows=1 width=36)
-> Seq Scan on t2 (cost=0.00..0.00 rows=1 width=36)

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