On 11/29/2018 10:47 AM, Alvaro Herrera wrote:
On 2018-Nov-28, Tom Lane wrote:
Alvaro Herrera <alvhe...@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.
I thought about just saving the search_path. It has all the necessary
information for a DBA or a developer, but creates problems for reporting
tools.
If we have the new query_qn column then we can group statistics by
query_qn and display it on the charts and graphs.
If instead we use a combination of query and search_path then a
reporting tools has to figure out the way to show both values to
distinguish between
different versions of query.
If it is easier/faster to add search_path then let's add search_path
instead of query_qn. It is already documented that query text isn't
unique by itself,
and reporting tools have to use query+queryid for uniqueness, and
search_path will provide the currently unavailable information to the
DBAs/developers.
Good.
