Anthony W. Youngman kirjutas P, 19.10.2003 kell 21:24:
>
> As soon as a requirement for a database specifies extraction of the
> maximum power from the box, it OUGHT to rule out all the current
> relational databases. MV flattens it for it for performance. As an MV
> programmer, I *KNOW* that I can find any thing I'm looking for (or find
> out it doesn't exist) with just ONE disk seek.
Relational or not, this requires either in-memory index or perfect hash.
BTW, how do you find the oldest red elephant "with just one disk seek"?
as in SQL:
select from elephants where colour=red order by age desc limit 1;
> A relational programmer
> has to ask the db "does this exist" and hope the db is optimised to be
> able to return the result quickly. To quote the Pick FAQ "SQL optimises
> the easy task of finding stuff in memory. Pick optimises the hard task
> of getting it into memory in the first place".
SQL by itself optimises nothing: by definition it evaluates full cross
products and then compares all rows with predicates.
Some SQL implementations do optimse a little ;)
> "Relational" is all about theory and proving things mathematically
> correct. "MV" is all about engineering and getting the result.
Or perhaps just getting _the_ result ;)
getting some other result will probably need another MV database ;)
> Unless you can use set theory to predict the future,
Isn't this what PostgreSQL's optimiser does ?
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Hannu