Guido,

> I have a empty DB and I insert several thousands of datasets. Now I open
> a query and it takes 0,1362 sec. Now I deactivate all my indices

<SNIP>

> Then I acivate all my indices

<SNIP>

> Now I open the query again and it takes nearly 4 sec.
>
> Have anybody a idea, what the reason is for this behaviour ?

my guess is that the rebuild operation has forced IB to get all the
index pages in the cache, thus eliminating your data pages which were
there at the beginning (when you inserted the data).

If this were true, you would experience a much smaller delay when trying
to open the query a third time.
HTH
--
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_/\/ando