Re: [PATCHES] VACUUM Improvements - WIP Patch

Abhijit Menon-Sen wrote:
> At 2008-08-25 10:24:01 +0300, heikki(at)enterprisedb(dot)com wrote:
>> My original plan was to enable index-only-scans using the DSM as well
>> for 8.4, but it's pretty clear at this point that I don't have the
>> time to finish that :-(.
>
> I wonder how hard that would be.

It's doable, for sure.

The pieces I see as required for that are:
1. change the indexam API so that indexes can return tuples
2. make sure the DSM is suitable for index-only-scans. Ie. it must be
completely up-to-date and WAL-logged, so that if the DSM says that all
tuples on a page are visible, they really must be.
3. planner/stats changes, so that the planner can estimate how much of
an index scan can be satisfied without looking at the heap (it's not an
all-or-nothing plan-time decision with this design)

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com