I am developing against 9.1beta3 and encountered this problem. I repeated it against rc1 (or actually, REL9_1_STABLE taken from git today).
The below SQL causes: TRAP: FailedAssertion("!(item_width > 0)", File: "costsize.c", Line: 3274) and the session crashes. select * from ( select col1 , col2 , reviewed from (values ( 1111, 'aweyu', 3) , ( 2222, 'bwetu', 2) , ( 3333, 'vwxyz', 1) ) as r(col1,col2,col3) left join ( select 1 as reviewed, c2 from ( values ('abcde') ) as t1(c2) union all select 0 as reviewed, c2 from ( values ('vwxyz') ) as t2(c2) ) as up_all on up_all.c2 = r.col2 order by col3 ) as f ; To simplify I used 'values' for the actual tables that I am using, but the above still causes the FailedAssertion. Removing the outer select avoids the error and removing order by avoids the error Erik Rijkers -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers