Re: JIT & function naming

On 2017-09-03 10:11:37 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > Currently there's essentially a per EState counter and the generated
> > functions get named deform$n and evalexpr$n. That allows for profiling
> > of a single query, because different compiled expressions are
> > disambiguated. It even allows to run the same query over and over, still
> > giving meaningful results. But it breaks down when running multiple
> > queries while profiling - evalexpr0 can mean something entirely
> > different for different queries.
>
> > The best idea I have so far would be to name queries like
> > evalexpr_$fingerprint_$n, but for that we'd need fingerprinting support
> > outside of pg_stat_statement, which seems painful-ish.
>
> Yeah. Why not just use a static counter to give successive unique IDs
> to each query that gets JIT-compiled? Then the function names would
> be like deform_$querynumber_$subexprnumber.

That works, but unfortunately it doesn't keep the names the same over
reruns. So if you rerun the query inside the same session - a quite
reasonable thing to get more accurate profiles - the names in the
profile will change. That makes it quite hard to compare profiles,
especially when a single execution of the query is too quick to see
something meaningful.

Greetings,

Andres Freund