--- In firebird-support@yahoogroups.com, Helen Borrie <helebor@...> wrote:

>
> At 05:13 25/09/2008, you wrote:
> >I have a table with columns and constraint
> >
> >x varchar(250)
> >y varchar(250)
> >z varchar(40)
> >UNIQUE (x, y, z)
> >
> >The charset is UTF8, so the key length is (250+250+40)*3 = 1620
> >
> >With a page size of 16384, no problem. With a page size of 8192, I
> >get the following error:
> >
> >key size exceeds implementation restriction for index "RDB$3"
> >
> >RDB$3 is the (x, y, z) constraint. According to the release notes
> >(Firebird_v2.0.3.ReleaseNotes.pdf), the maximum key size should be 1/4
> >the page size. For 8192, this would be 2048. What am I missing?
>
> It's not a matter of just adding up the widths and comparing them

with the limit. Composite indices take up more "width", as do
multi-byte charsets and collations. In your example the total key
size is 2700 bytes, so you need to adjust the widths of those varchars
if you want a unique constraint on them with an 8K page size.

>
> How do I know your key size? visit

http://www.volny.cz/iprenosil/interbase/ip_ib_indexcalculator.htm

>
> ./heLen
>

Very enlightening! Thank you!