Re: Should duplicate indexes on same column and same table be allowed?

On 12/9/06, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "Rajesh Kumar Mallah" <mallah(dot)rajesh(at)gmail(dot)com> writes:
> > Some of our tables have duplicate indexes on same column by different
> > index names.
> > Should the database server check for the existance of (effectively)
> > same index in
> > a table before creating a new one.
>
> I'd vote not; I think this would get in the way of people who do know
> what they're doing, as much as it would hold the hands of those who
> don't. ("Build a database that even a fool can use, and only a fool
> would want to use it.")
>
> An example: suppose you mistakenly created a plain index on foo.bar,
> when you meant it to be a unique index. You don't want to just drop the
> plain index before creating a unique index, because you have live
> clients querying the table and their performance would tank with no
> index at all. But surely a plain index and a unique index on the same
> column are redundant, so a nannyish database should prevent you from
> creating the desired index before dropping the unwanted one.

I meant *exactly* the same index (pls ignore the word effectively in prv post).
even same tablespace.

Regds
mallah.

PS: (forgive me for my meager knowledge of internals)

>
> Other scenarios: is an index on X redundant with one on X,Y? Is a hash
> index on X redundant if there's also a btree index on X? How about
> partial or functional indexes with slightly varying definitions?
>
> There's been some discussion lately about an "index advisor", which
> might reasonably provide some advice if it thinks you have redundant
> indexes. But I'm not eager to put any sort of enforcement of the point
> into the core database.
>
> regards, tom lane
>