What kind of index to use for many rows with few unique values?

Hi,

I have a table with a column called "state". Each row can be in one
of four states, let's call them 'new', 'pending', 'ok', and 'bad'.
On average, about 95% of the rows will be 'bad', with the remaining
5% being in one of the other three states. If the table has 50K rows
and I just want to pull out the 'ok' rows, I don't want to do a sequential
scan. To pull out the 'bad' rows, obviously, sequential scan is fine.

I've heard that a btree index performs badly in this situation. Is
a hash index appropriate? I've heard bad things about hash indexes in
PostgreSQL.

Regards,

David.

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