Re: [GENERAL] Idea for the statistics collector

Martijn van Oosterhout wrote:
> Since it's currently all for collecting statistics on tables, why can't it
> collect another type of statistic, like:
> 
> - How often the estimator gets it wrong?
> 
> At the end of an index scan, the executor could compare the number of rows
> returned against what was estimated, and if it falls outside a certain
> range, flag it.
> 
> Also, the average ratio of rows coming out of a distinct node vs the number
> going in.
> 
> For a join clause, the amount of correlation between two columns (hard).
> 
> etc
> 
> Ideally, the planner could then use this info to make better plans.
> Eventually, the whole system could become somewhat self-tuning.
> 
> Does anyone see any problems with this?

[ Discussion moved to hackers.]

I have thought that some type of feedback from the executor back into
the optimizer would be a good feature.  Not sure how to do it, but your
idea makes sense.  It certainly could update the table statistics after
a sequential scan.

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