Re: Two efficiency questions - clustering and ints

John D. Burger wrote:
> I have a good-size DB (some tables approaching 100M rows), with
> essentially static data.
>
> Should I always cluster the tables? That is, even if no column jumps
> out as being involved in most queries, should I pick a likely one and
> cluster on it? (Of course, this assumes that doing so won't cause bad
> correlation with any other oft-used column.)

Well you cluster on an index, and if you don't think the index is
useful, I'd drop it. If you have an index, clustering isn't necessarily
going to help you unless you regularly read a series of rows in order.

> Another question, about integer types - if no cross-type coercion is
> involved, is there any reason not to choose the smallest int type that
> will fit my data? In particular, I have a column of small-integer
> ratings with, say, values in [1, 10]. If I'm only comparing within such
> ratings, and possibly computing floating point averages, etc., what are
> the good and bad points of using, say, SMALLINT? What about NUMERIC(1)
> or (2)?

(int2, int2) should pack into 4 bytes on-disk, but due to alignment
issues I think (int2, int4) still takes up 8 bytes. There has been
discussion about being able to have different physical column ordering
on-disk vs. in SQL but no decision as to whether the effort will be
worthwhile.

Numeric types tend to be slower than their int equivalent, and though
I've not checked their storage requirements, I'd assume they take more
space too.

HTH
--
Richard Huxton
Archonet Ltd