How do I find what is calling pg_read_file
As said, check the log's to find DB,Host,User etc. from where its been called. If log_line_prefix not set to appropriate to all those details then change it as shown below which just need RELOAD of server. After changing your logs should show those details. Eg:-
log_line_prefix = '%t [%p]: [%l-1] db=%d,user=%u client=%h'
Also, its just my guess, if pg_read_file() function called from any other function then you can check with below query.
select proname from pg_proc where prosrc ilike '%pg_read_file%' and pronamespace=(select oid from pg_namespace where nspname='public');
---
