On Tue, 2003-04-08 at 00:18, Jim C. Nasby wrote:
> 'visibility information'? Is this related to the versioning that pgsql
> uses instead of read locks?
Yes -- it's the information used by PostgreSQL to implement MVCC.
> I know in other RDBMS's it's very useful to
> have index covering because it eliminates needing to load the base pages
> into memory at all
Storing visibility information in index entries (in addition to heap
tuples) doesn't strike me as a good idea: for one thing, an
UPDATE/DELETE would require touching both heap tuples and any index
entries that point to them. It would also bloat the size of indexes.
Cheers,
Neil