On Tuesday 30 October 2001 21:24, Alex Pilosov wrote:
> > > | The consequence for my problem is now: If it is technically possible
> > > | to implement index scans without table lookups please implement it.
> > > | If
> The feature you are looking for is called 'index coverage'. Unfortunately,
> it is not easy to implement with Postgresql, and it is one of few
> outstanding 'nasties'. The reason you can't do it is follows: Postgres
> uses MVCC, and stores 'when' the tuple is alive inside the tuple. So, even
> if index contains all the information you need, you still need to access
> main table to check if the tuple is valid.
> Possible workaround: store tuple validity in index, that way, a lot more
> space is wasted (16 more bytes/tuple/index), and you will need to update
> all indices when the base table is updated, even if indexed information
> have not changed.
What is the problem to implement this index as a special index type for
people who need this? Just add a flag keyword to index creation clause.
Actually I would like to hear Tom's opinion on this issue. This issue is of
my interest too.
Also I saw sometime ago in hackers that there is a patch implementing this...
Or I am wrong here?
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