Function ExecAggTransReparent

src/backend/executor/execExprInterp.c:4447–4488

* Ensure that the current transition value is a child of the aggcontext, * rather than the per-tuple context. * * NB: This can change the current memory context. */

 * NB: This can change the current memory context.
 */
Datum
ExecAggTransReparent(AggState *aggstate, AggStatePerTrans pertrans,
					 Datum newValue, bool newValueIsNull,
					 Datum oldValue, bool oldValueIsNull)
{
	Assert(newValue != oldValue);

	if (!newValueIsNull)
	{
		MemoryContextSwitchTo(aggstate->curaggcontext->ecxt_per_tuple_memory);
		if (DatumIsReadWriteExpandedObject(newValue,
										   false,
										   pertrans->transtypeLen) &&
			MemoryContextGetParent(DatumGetEOHP(newValue)->eoh_context) == CurrentMemoryContext)
			 /* do nothing */ ;
		else
			newValue = datumCopy(newValue,
								 pertrans->transtypeByVal,
								 pertrans->transtypeLen);
	}
	else
	{
		/*
		 * Ensure that AggStatePerGroup->transValue ends up being 0, so
		 * callers can safely compare newValue/oldValue without having to
		 * check their respective nullness.
		 */
		newValue = (Datum) 0;
	}

	if (!oldValueIsNull)
	{
		if (DatumIsReadWriteExpandedObject(oldValue,
										   false,
										   pertrans->transtypeLen))
			DeleteExpandedObject(oldValue);
		else
			pfree(DatumGetPointer(oldValue));
	}

	return newValue;
}

/*
 * Invoke ordered transition function, with a datum argument.