>
> Since you have declared the column 'key' as PRIMARY KEY there
> is an index on column 'key' anyway and SELECT value FROM
> small where key = 12345 will use that index: on my system psql said:
>
> omicron=# EXPLAIN SELECT value FROM small WHERE key = 12345;
> NOTICE: QUERY PLAN:
>
> Index Scan using small_pkey on small (cost=0.00..8.14
> rows=10 width=12)
>
> > Since it can get the answer straight out of the index, and if there
> > are potentially numerous rows, looking up a b-tree is faster than a
> > linear search?
>
> Looking up from an index is of course faster than a seq. scan
> (in almost all cases).
Hrmm... I have 26 rows in mine at the moment, and after vacuum
analyzing, it uses a seq. scan. How come yours used the index? I
thought mine wasn't using an index because postgres won't use an index
until the table is "big enough".
But if an index page is already in cache.. surely it'd be faster using
it than doing a seq. scan.
(Yes, I know its a small table, but I think the worst case for seq. scan
would be a fair bit worse than for the index, and every little bit
counts, right?)
- Andrew