On 24.08.2017 14:56, Adrien Nayrat wrote:
Hi hackers,
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Hi,
I try to made a patch to auto_explain in order to log queries with
wrong estimation.
I compare planned row id : queryDesc->planstate->plan->plan_rows
Vs ntuples : queryDesc->planstate->instrument->ntuples;
AFAICS you want to introduce two additional per-node variables:
- auto_explain_log_estimate_ratio that denotes minimum ratio (>= 1)
between real value and planned one. I would add 'min' prefix before
'ratio'.
- auto_explain_log_estimate_min_rows - minimum absolute difference
between those two values. IMHO this name is somewhat poor, the suffix
'min_diff_rows' looks better.
If real expressions (ratio and diff) exceed these threshold values both,
you log this situation. I'm right?
If I understand, instrumentation is used only with explain. So my
patch works
only with explain (and segfault without).
Instrumentation is initialized only with analyze (log_analyze is true)[1]
Is there a simple way to get ntuples?
It's interesting question. In one's time I didn't find any way to get
the amount of tuples emitted from a node.
1. contrib/auto_explain/auto_explain.c:221
--
Regards,
Maksim Milyutin
