Re: Which indexes does a query use?

Chris Velevitch wrote:

> Are you saying that the strategy pg uses is dynamic, in that as the
> size of the table grows the strategy changes?

The planner is quite dynamic, and what strategy it comes up with will 
depend not just on the size of the table, but other things as well, 
even on the particular constants in your comparisons.  For instance, I 
think your original query had:

   where activity_user_id = 2

If the table statistics show that 2 is a very common value for that 
column, the planner will not use the index, as it will not save enough. 
  (I think I have that right.)

- John D. Burger
   MITRE