Re: how to implement selectivity injection in postgresql

On 13-08-2014 13:33, Rajmohan C wrote:
> SELECT c1, c2, c3, FROM T1, T2, T3
> WHERE T1.x = T2.x AND
> T2.y=T3.y AND
> T1.x >= ? selectivity 0.00001 AND
> T2.y > ? selectivity 0.5 AND
> T3.z = ? selectivity 0.2 AND
> T3.w = ?
>
> I need to implement Selectivity injection as shown in above query in
> PostgreSQL by which we can inject selectivity of each predicate or at least
> selectivity at relation level directly as part of query. Is there any
> on-going work on this front? If there is no ongoing work on this, How
> should I start implementing this feature?
>
Do you want to force a selectivity? Why don't you let the optimizer do
it for you? Trust me it can do it better than you. If you want to force
those selectivities for an academic exercise, that information belongs
to catalog or could be SET before query starts.

Start reading backend/optimizer/README.

--
Euler Taveira Timbira - http://www.timbira.com.br/
PostgreSQL: Consultoria, Desenvolvimento, Suporte 24x7 e Treinamento