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


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