On 9 January 2012 19:45, Josh Berkus <josh@agliodbs.com> wrote:
>> Obviously, many indexes are unique and thus won't have duplicates at
>> all. But if someone creates an index and doesn't make it unique, odds
>> are very high that it has some duplicates. Not sure how many we
>> typically expect to see, but more than zero...
>
> Peter may not, but I personally admin lots of databases which have
> indexes on values like "category" or "city" which have 100's or 1000's
> of duplicates per value. I don't think this is uncommon at all.
Uh, then all the more reason to do what I recommend, I imagine. There
is most definitely a large overhead to creating such indexes, at least
for scalar types. As far as I can tell, Tom's complaint is quite
speculative.
--
Peter Geoghegan http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training and Services