Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> On Fri, 2010-03-19 at 01:59 +0530, Gokulakannan Somasundaram wrote:
>> I believe it is very difficult to make visibility map update friendly
>> without compromising durability. But such a functionality is very
>> much wanted in PG still.
> Surely the VM is already update-friendly. If you update a tuple in a
> page with the visibility bit set, the bit must be unset or you will get
> wrong results.
The VM is (a) not compressed and (b) not correctness-critical.
Wrong bit values don't do any serious damage.
regards, tom lane