Re: Index on two columns not used

Heikki Linnakangas a écrit :
> Arnaud Lesauvage wrote:
>> This query was taken from my "adminsitrative areas" model (continents,
>> countries, etc...). Whenever I query this model, I have to join many
>> tables.
>> I don't really know what the overhead of reading the heap-tuples is, but
>> would it be a good idea to add data-redundancy in my tables to avoid
>> joins ? (adding country_id, continent_id, etc... in the "cities" table)
>
> It depends. I would advise not to denormalize unless you really really
> have to. It's hard to say without more knowledge of the application.
>
> Is the query you showed a typical one? It ran in about 160 ms, is that
> good enough? It's doesn't sound too bad, considering that it returned
> almost 40000 rows.

It is quite typical, yes. It is the base query of a view. In
fact, most views have a lot more joins (they join with all
the upper-level tables).
But 150ms is OK, indeed.