partial index on boolean, problem with v8.0.0rc1

Hi all,

PostgreSQL v8.0.0rc1, two variants of a "user_msg" table:

create table user_msg (
message_id integer not null references message(id) on update cascade on
delete cascade,
user_id integer not null,
status smallint not null default 0,
is_read boolean not null default false,
unique (message_id,user_id)
);
create index user_msg_is_read_idx on user_msg(is_read) where is_read=true;

create table user_msg (
message_id integer not null references message(id) on update cascade on
delete cascade,
user_id integer not null,
status smallint,
is_read boolean,
unique (message_id,user_id)
);
create index user_msg_is_read_idx on user_msg(is_read) where is_read=true;

In both cases, tables are filled with ~10m of rows, "is_read" is false in the
1st case, and "NULL" in the 2nd. I did "VACUUM FULL ANALYSE" after both
imports.

Here's the problem: in the 2nd case, planner wouldn't choose an index scan
using partial index on "is_read" for the following queries:

explain select * from user_msg where is_read=true;
explain select * from user_msg where is_read is true;
explain select * from user_msg where is_read;

In the 1st case, partial index was used for the first query.

--
Best Regards,
Igor Shevchenko