> I have an application which is writing every second the same record in
> a table with many colums. Each update is commited. I can observe that
> the memoryusage of fbserver increases and after a few hours windows
> starts to swap. fbserver uses 100% of CPU and the whole system stops.
> I'm using firebird 1.5 under Win XP.

If it so simple - can you create a test case for this ?
What is exact FB version ?

> Difference of oldest transaction, oldest active transaction and next
> transaction is 1

What about oldest snapshot transaction ? Also you can run gstat -r
to see how many versions you have

Regards,
Vlad