> a) We are already going from table to index to do unique checks. This is the
> same thing, which we will do to go and update the snapshot in the indexes.
No, it is not the same thing. Updating index snapshots requires being
able to *re-find* a previously made index entry for the current row.
And it has to be done 100% reliably. The worst that happens if an index
entry is not found when it should be during a uniqueness check is that
the uniqueness constraint is not enforced properly; which is bad but it
doesn't lead to internally-inconsistent data structures.
Tom,
We are also going to indexes to maintain the referential integrity constraints like foreign keys. Say there are constraints like 'On Delete Cascade' and 'On Delete Restrict', they are maintained through the indexes and if we say that indexes can return wrong results, then the referential integrity is lost and we no longer are ACID compliant.
Thanks,
Gokul.