Hi Dmitry,

Thanks for the swift reply.

> While not being strictly required, this is usually recommended.

Good to know - thanks!

> Do you update the index statistics regularly, especially when the EVENT
> table goes from 10M to 40M records?

Yes - I made quite sure to recalculate statistics on both tables. Once statistics are recalculated, switching between 2.1.1 and 2.1.2 produces two different plans (no inserts or updates between version changes).

> http://tracker.firebirdsql.org/browse/CORE-2411

That looks very much related to my problem. My apologies for missing that in the tracker!

Thanks,
David