Timothy Madden wrote:

>
> Firebird really uses fixed-length records ?

No, it uses run-length compression on records, and stores
most back versions as differences from the more recent version.
However, for the purpose of guessing at table cardinality for
the optimizer, it uses the record length as a guess - guessing
large on records makes up for page overhead, record overhead,
and back versions, generally. Besides, the optimizer really
cares more about how many pages have to be read than how many
records - I/O is so much more expensive than memory manipulations...

>
> so nRecCount = nPages * (nPageSize / nRecSize) ?

No, the records are compressed, and as above, even with records
that don't compress, you'd have to consider page and record
overhead.

>
> Are fixed-length records not a bad thing ?

Yes they are, in general, though MySQL seems to survive with
them.


Cheers,

Ann