Leos,

>It looked as if FB does not use cache data. What to set?

I don't know - just thought I should answer since no-one seems to have done
so.

>select sum(price) from inv_rows, inv_heads, companies
>where inv_rows.invcode=inv_heads.invcode and
>inv_heads.compid=companies.compid and
>companies.compname like 'A%'

This isn't the best SQL for IBO - it may work OK if you set JoinLinks, but
it is simpler to just use the JOIN syntax:

select sum(price) from inv_rows
join inv_heads on inv_rows.invcode=inv_heads.invcode
join companies on inv_heads.compid=companies.compid
where companies.compname like 'A%'

What kind of indexes does your select use? An index on compname might be
benefitial for this select (but I think it requires you to not use a
parameter - if so, see if LIKE can be replaced with STARTING WITH.

HTH,
Set