Re: compute_query_id and pg_stat_statements

On Fri, May 14, 2021 at 3:12 AM Bruce Momjian <bruce@momjian.us> wrote:
>
> > Maybe we should revert this thing pending somebody doing the work to
> > make a version of queryid labeling that actually is negligibly cheap.
> > It certainly seems like that could be done; one more traversal of the
> > parse tree can't be that expensive in itself.  I suspect that the
> > performance problem is with the particular hashing mechanism that
> > was used, which looks mighty ad-hoc anyway.
>
> I was surprised it was ~2%.

Just to be clear, the 2% was a worst case scenario, ie. a very fast
read-only query on small data returning a single row.  As soon as you
get something more realistic / expensive the overhead goes away.  For
reference here is the detail:
https://www.postgresql.org/message-id/CAOBaU_ZVmGPfKTwZ6cM_qdzaF2E1gMkrLDMwwLy4Z1JxQ6=CZg@mail.gmail.com