How to copy Datum

Hi,

I'm trying to reduce the re-computing of window aggregation. Here the
AVG function for example.

The original window aggregation's transition value(transValue) of AVG is
an ArrayType, that contains two main values(sum, count).

Now, I'm using a temporary transition value (tempTransValue), and I need
to copy tempTransValue to the original window aggregation's transition
value(transValue).

I used the function datumCopy as following:

peraggstate->transValue = datumCopy(peraggstate->tempTransValue,
peraggstate->transtypeByVal, peraggstate->transtypeLen);

But when the copied transValue is passed to the invoke function, here is
int4_avg_accum, the ArrayType returned from PG_GETARG_ARRAYTYPE_P(0) is
null.

Which means the copy action is failed.

Anybody know why? Or give me some suggestions? Thanks very much.

Best Regards

Chaoyong Wang