Robert Haas napsal(a):
Let's suppose, for example, that in 8.5 we decide to change some type
that is presently 16 bits to 32 bits, or 8 bits to 16 bits, etc. This
will make some tuples bigger, and potentially much bigger, but since
it presumably won't be a commonly used data-type, most tuples won't
change at all. However, the worst case scenario for how much free
space you might need to reserve will be very bad, and therefore a
mechanism that allows reserving a fixed amount of free space per page
won't be adequate.
The problem with datatypes is different story. It is should be easy to manage
this problem with keeping the old datatype definition for "old" tables and for
new create new datatype with new OID. You can use ALTER TABLE for converting
data from old type to the new one.
Zdenek
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