Re: estimating # of distinct values

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Tue, Jan 18, 2011 at 12:23 PM, Jim Nasby <jim(at)nasby(dot)net> wrote:
>> On Jan 17, 2011, at 8:11 PM, Robert Haas wrote:
> On Mon, Jan 17, 2011 at 7:56 PM, Jim Nasby <jim(at)nasby(dot)net> wrote:
>>> - Forks are very possibly a more efficient way to deal with TOAST than having separate tables. There's a fair amount of overhead we pay for the current setup.
>
> That seems like an interesting idea, but I actually don't see why it
> would be any more efficient, and it seems like you'd end up
> reinventing things like vacuum and free space map management.
>>
>> The FSM would take some effort, but I don't think vacuum would be that hard to deal with; you'd just have to free up the space in any referenced toast forks at the same time that you vacuumed the heap.

> How's that different from what vacuum does on a TOAST table now?

Even more to the point: Jim hasn't provided one single reason to suppose
that this would be better-performing than the existing approach. It
looks to me like a large amount of work, and loss of on-disk
compatibility, for nothing at all except the sake of change.

regards, tom lane