explain analyze
select *
from test.features
where to_tsquery('') @@ features.vector
ERROR: Gin doesn't support full scan due to it's awful inefficiency
Look:
contrib_regression=# select '{1,2,3}'::int4[] @ '{}'; --contains
?column?
----------
t
(1 row)
contrib_regression=# select '{1,2,3}'::int4[] && '{}'; --overlap
?column?
----------
f
(1 row)
contrib_regression=# select to_tsvector('asdasd') @@ ''::tsquery;
NOTICE: query doesn't contain lexeme(s)
?column?
----------
f
(1 row)
Semantic of different operation with void (but not NULL) argument is very
different. If query doesn't contain any entry (returned by extractQuery() index
support method), then GIN, in any case, doesn't know what it should return:
whole set of pointers or nothing. But GIN can't return all - it will be
very-very slow, because there is a lot of pointers in GIN index to each table's row.
It seems to me that message makes confuse about reason of error...
Interestingly this works:
explain analyze
select *
from test.features
where NULL @@ features.vector
That is because @@ is marked as 'returns NULL on NULL input', ie index will not
be used.
--
Teodor Sigaev E-mail: teodor@xxxxxxxxx
WWW: http://www.sigaev.ru/
