Re: Why does increasing the precision of a numeric column rewrites the table?

Thomas Kellerer <spam_eater(at)gmx(dot)net> writes:
> I don't understand why going from numeric(12,2) to numeric(15,3) would require a table rewrite.

The comment for numeric_transform explains this:

* Flatten calls to numeric's length coercion function that solely represent
* increases in allowable precision. Scale changes mutate every datum, so
* they are unoptimizable. Some values, e.g. 1E-1001, can only fit into an
* unconstrained numeric, so a change from an unconstrained numeric to any
* constrained numeric is also unoptimizable.

The issue is basically that changing '1.00' to '1.000' requires a change
in the actually-stored value.

regards, tom lane