sorry for small offtopic. Can be used this mechanism for log of executed plan or full query?
That's a really good idea. I'd love to be able to pg_explain_backend(...)
I left the mechanism as a generic diagnostic signal exactly so that we could add other things we wanted to be able to ask backends. I think a follow-on patch that adds support for dumping explain-format plans would be great, if it's practical to do that while a query's already running.
Noticing the interest in the calling some routines on the remote backend through signals, in parallel thread[1] I have proposed the possibility to define user defined signal handlers in extensions. There is a patch taken from pg_query_state module.
