>> You did not write, which server version you are using and on which
>> hardware.
>
> FB 2.5.2.26539
>
>> I have one intensively used ClassicServer 1.5.6 (...yeah... *am* in
>> the process of migrating to 2.5.2) running on a dedicated machine with
>> Windows2003 OS. 4 GB Ram only, which seems ridiculously little today.
>
> Never feel bad about using old hardware or old FB. FB is very efficient and doesn't need a whole lot. If the user group is happy, FB version is not relevant.
>
> Each time the stored proc is run it has to delete about 30K records and add just over a million records.

* Garbage collection might kick in here
* Updating active indexes takes time as well, especially with a small
page cache. Perhaps you can deactivate indexes before running the SP and
activate them afterwards?
* Depending on how you get your records for inserting, this might be
inefficient due to a bad PLAN (missing index, bad index, out-dated
statistics)
* Are you using EXECUTE STATEMENT in your SP


--
With regards,
Thomas Steinmaurer
http://www.upscene.com/