Re: [HACKERS] [FEATURE PATCH] pg_stat_statements with plans

Alright, for the next version of this patch I'll look into standard 
deviation (an implementation of Welfords' algorithm already exists in 
pg_stat_statements).

On 3/4/17 14:18, Peter Eisentraut wrote:

> The other problem is that this measures execution time, which can vary
> for reasons other than plan.  I would have expected that the cost
> numbers are tracked somehow.
I've already thought of tracking specific parts of the explanation, like 
the cost numbers, instead of the whole string, I'll think of something, 
but if anybody has any bright ideas in the meantime, I'd gladly listen 
to them.

> There is also the issue of generic vs specific plans, which this
> approach might be papering over.
Would you be so kind and elaborate a little bit on this? I'm not sure if 
I understand this correctly. This patch only tracks specific plans, yes. 
The inital idea was that there might be some edge-cases that are not 
apparent when looking at generalized plans or queries.

kind regards
Julian