questions - WAL And Sets, Lists, Ref

Hi,
I have asked this question before but I have n't got any answers
yet.

Question 1.

Since postgres only inserts records instead of updating rows. It is
possible that records for a particular
table may not be found on the same page. This can slow down the
processing of the queries.

Has anybody experienced this problem before? Is it possible to
happen?

How is the performance of VACCUM?

Question 2.

How are "OO" features in PostgreSql? Does anybody have any examples
to refer to?

I have found only "create type", "arrays".

But. what about lists, sets etc?

I would appreciate answers to these questions.

Regards,
Sandeep