On 2018-Nov-28, Tom Lane wrote:
> Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> > On 2018-Nov-28, Tom Lane wrote:
> >> This would also entail rather significant overhead to find out schema
> >> names and interpolate them into the text.
>
> > True. I was thinking that the qualified-names version of the query
> > would be obtained via ruleutils or some similar mechanism to deparse
> > from the parsed query tree (not from the original query text), where
> > only pg_catalog is considered visible. This would be enabled using a
> > GUC that defaults to off.
>
> Color me skeptical --- ruleutils has never especially been designed
> to be fast, and I can't see that the overhead of this is going to be
> acceptable to anybody who needs pg_stat_statements in production.
> (Some admittedly rough experiments suggest that we might be
> talking about an order-of-magnitude slowdown for simple queries.)
Good point.
Maybe we can save the OID array of schemas that are in search_path when
the query is first entered into the statement pool, and produce the
query_qn column only at the time the entry is interpreted (that is, when
pg_stat_statements is query). ... oh, but that requires saving the plan
tree too, which doesn't sound very convenient.
Maybe just storing the search_path schemas (as Tomas already suggested)
is sufficient for Sergei's use case? Do away with query_qn as such, and
just have the user interpret the names according to the stored
search_path.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
