Re: pg_stat_statements fingerprinting logic and ArrayExpr

On Tue, Dec 10, 2013 at 2:38 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> It's very hard to see where you should spend efforts when every "logical
> query" is split into hundreds of pg_stat_statement entries. Suddenly
> it's important whether a certain counts of parameters are more frequent
> than others because in the equally distributed cases they fall out of
> p_s_s again pretty soon. I think that's probably a worse than average
> case, but certainly not something only I could have the bad fortune of
> looking at.

Another problem is that creating a new entry is relatively expensive,
because we need to acquire an exclusive lock to do so. If there was a
lot of churn, I'd worry that the performance overhead of
pg_stat_statements. It could be quite a lot higher than necessary.

--
Peter Geoghegan