Postgres: log_statement = 'none' is ignored when query comes from C++ - postgresql

Question

I am blocked by the following problem.
The log_statement of postgres on a server is set to ddl (or all). The database is created by my application, written in C++. Queries are sent to DB by using libpq - PQexec.
Every query is logged twice, i don't know why (I am not a C++ programmer nor expert in postgres):
Apr 3 02:26:44 xxx postgres[12345]: [8-1] [2020-04-03 02:26:44.487 CDT] [s:xxx.694d] [u:user] [a:[unknown]] [db:postgres] [p:12345] [clnt:[local]] LOG: statement: CREATE USER "gingillo" WITH PASSWORD 'giggio';
Apr 3 02:26:44 xxx postgres[12345]: [9-1] [2020-04-03 02:26:44.487 CDT] [s:xxx.694d] [u:user] [a:[unknown]] [db:postgres] [p:12345] [clnt:[local]] LOG: AUDIT: SESSION,1,1,ROLE,CREATE ROLE,,,"CREATE USER ""gingillo"" WITH PASSWORD <REDACTED>",<not logged>
As you already imaged, I don't want to log passwords, so I changed the current query (1):
CREATE USER "gingillo" WITH PASSWORD 'giggio'
to be following (2):
BEGIN;SET LOCAL log_statement = 'none';CREATE USER "gingillo" WITH PASSWORD 'giggio';COMMIT;
If I run manually the query (2), I get the result I want, just one log is logged containing REDACTED instead of the password:
Apr 3 02:26:44 xxx postgres[12345]: [9-1] [2020-04-03 02:26:44.487 CDT] [s:xxx.694d] [u:user] [a:[unknown]] [db:postgres] [p:12345] [clnt:[local]] LOG: AUDIT: SESSION,1,1,ROLE,CREATE ROLE,,,"CREATE USER ""gingillo"" WITH PASSWORD <REDACTED>",<not logged>
But when the same query is run by C++, I have double log, showing even the log_statement stuff:
Apr 8 06:44:24 xxx postgres[27171]: [8-1] [2020-04-08 06:44:24.489 CDT] [s:xxx.6a23] [u:user] [a:[unknown]] [db:postgres] [p:27171] [clnt:[local]] LOG: statement: BEGIN;SET LOCAL log_statement = 'none';CREATE USER "gingillo" WITH PASSWORD 'giggio';COMMIT;
Apr 8 06:44:24 xxx postgres[27171]: [9-1] [2020-04-08 06:44:24.490 CDT] [s:xxx.6a23] [u:user] [a:[unknown]] [db:postgres] [p:27171] [clnt:[local]] LOG: AUDIT: SESSION,1,1,ROLE,CREATE ROLE,,,"BEGIN;SET LOCAL log_statement = 'none';CREATE USER ""gingillo"" WITH PASSWORD <REDACTED>",<not logged>
Does anybody have any idea how to disable the first log? What am I doing wrong?

Answer 1

SET LOCAL scope is only for the current transaction.
Try:
Either to run SET log_statement=none that persists during the database session unless ROLLBACK is issued.
or to run SET LOCAL log_statement=none for each transaction.
It looks C++ code is setting log_statement parameter: the best solution should be to remove it since it already uses another logging.

Answer 2

You are sending PostgreSQL a single "statement" which contains 4 actual statements. By the time the "SET LOCAL log_statement = 'none'" is processed, the damage has already been done as the entire multi-statement statement has already been logged. You need to send each statement separately if you want to have part of it effect the settings for the other part of it.
Alternatively, just avoid setting log_statement to 'all' in the first place, as it seems to be unneeded.