Re: pg_stat_statements: calls under-estimation propagation

>This patch needs documentation. At a minimum, the new calls_underest
>field needs to be listed in the description of the pg_stat_statements.
I have attached a version which includes documentation.
pg_stat_statements-identification-v4.patch.gz
<http://postgresql.1045698.n5.nabble.com/file/n5770844/pg_stat_statements-identification-v4.patch.gz>  
>Pardon for not following the discussion: What exactly does the
>calls_underest field mean? I couldn't decipher it from the patch. What
>can an admin do with the value? How does it compare with just bumping up
>pg_stat_statements.max? 
Paraphrasing the documentation. 
There is a possibility that,for queries which are tracked intermittently,
could have their statistics silently reset.
The calls_underest field gives an indication that a query has been tracked
intermittently and consequently have a higher probability of erroneous statistics. Queries tracked
constantly will have a zero value for 
calls_underest indicating zero probability of erroneous statistics.
A greater value of calls_underest indicates greater degree of inconsistent
tracking which in
turn means greater possibility of erroneous statistics due to statistics
being reset when 
query was not being tracked.

Increasing pg_stat_statements.max reduces the possibility of a query being
tracked intermittently but does not address the problem of indicating the
probability of erroneous statistics if the query is indeed being tracked
intermittently. I do not believe the admin can influence the value of 
calls_underest as it is not a GUC parameter.

We have a need to see this patch committed hence the revived interest in
this thread

regards
Sameer



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