"Pavan Deolasee" <pavan.deolasee@gmail.com> writes:
> HOT update is feasible iff
>
> - old and new tuples, both match the partiality condition OR
> - old and new tuples, both don't match the condition
...
> For functional index, we should apply the function to the old and new
> tuple and compare the outcome. If the results are same, HOT update
> is feasible.
This is debatable. We could compare the columns used in the partial condition
expression or function expression directly. If they're the same then the
expression or function must return the same value. If the function is quite
expensive then that might be cheaper.
On the other hand if it's not expensive and the columns change frequently but
the results don't then we might be doing a lot of work for nothing.
-- Gregory Stark EnterpriseDB http://www.enterprisedb.com