Tom Lane wrote:
>
> Jean-Luc Lachance <jllachan@nsd.ca> writes:
> > What would be involved in adding version and visibility to the index?
>
> * Index bloat. An index entry is currently 8 bytes plus the index key,
> eg 12 bytes for an int4 index. Version info would add 12 bytes.
> Doubling the size of indexes would double the time for index scans.
That is true for for small keys, but for varchar(20) the impact is less.
>
> * Update costs. Instead of one place to update when a row is updated,
> now all the associated index entries would have to be updated too.
The index has to be updated anyhow to reflect the new record. Doesn't
it?
>
> regards, tom lane